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[paraslash.git] / web / manual.m4
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9 define(`REFERENCE', ./``#''`LOCAL_LINK_NAME($1)' (`REMOVE_NEWLINE($2)'))
10 define(`XREFERENCE', `$1' (`REMOVE_NEWLINE($2)'))
11 define(`EMPH', ``_''`REMOVE_NEWLINE($1)'``_'')
12
13 Paraslash user manual
14 =====================
15
16 This document describes how to install, configure and use the paraslash
17 network audio streaming system. Most chapters start with a chapter
18 overview and conclude with an example section. We try to focus on
19 general concepts and on the interaction of the various pieces of the
20 paraslash package. Hence this user manual is not meant as a replacement
21 for the manual pages that describe all command line options of each
22 paraslash executable.
23
24 ------------
25 Introduction
26 ------------
27
28 In this chapter we give an REFERENCE(Overview, overview) of the
29 interactions of the two main programs contained in the paraslash
30 package, followed by REFERENCE(The paraslash executables, brief
31 descriptions) of all executables.
32
33 Overview
34 ~~~~~~~~
35
36 The core functionality of the para suite is provided by two main
37 executables, para_server and para_audiod. The former maintains a
38 database of audio files and streams these files to para_audiod which
39 receives and plays the stream.
40
41 In a typical setting, both para_server and para_audiod act as
42 background daemons whose functionality is controlled by client
43 programs: the para_audioc client controls para_audiod over a local
44 socket while the para_client program connects to para_server over a
45 local or remote networking connection.
46
47 Typically, these two daemons run on different hosts but a local setup
48 is also possible.
49
50 A simplified picture of a typical setup is as follows
51 <<
52 <pre>
53 server_host client_host
54 ~~~~~~~~~~~ ~~~~~~~~~~~
55
56 +-----------+ audio stream +-----------+
57 |para_server| -----------------------------> |para_audiod|
58 +-----------+ +-----------+
59 ^ ^
60 | |
61 | | connect
62 | |
63 | |
64 | +-----------+
65 | |para_audioc|
66 | +-----------+
67 |
68 |
69 | connect +-----------+
70 +-------------------------------------- |para_client|
71 +-----------+
72 </pre>
73 >>
74
75 The paraslash executables
76 ~~~~~~~~~~~~~~~~~~~~~~~~~
77
78 *para_server*
79
80 para_server streams binary audio data (MP3, OGG/Vorbis, OGG/Speex,
81 M4A, WMA files) over local and/or remote networks. It listens on a
82 TCP port and accepts commands such as play, stop, pause, next from
83 authenticated clients. There are many more commands though, see the
84 man page of para_server for a description of all commands.
85
86 It supports three built-in network streaming protocols
87 (senders/receivers): HTTP, DCCP, or UDP. This is explained in more
88 detail in the section on REFERENCE(Networking, networking).
89
90 The built-in audio file selector of paraslash is used to manage your
91 audio files. It maintains statistics on the usage of all available
92 audio files such as last-played time, and the number of times each
93 file was selected.
94
95 Additional information may be added to the database to allow
96 fine-grained selection based on various properties of the audio file,
97 including information found in (ID3) tags. However, old-fashioned
98 playlists are also supported.
99
100 It is also possible to store images (album covers) and lyrics in the
101 database and associate these to the corresponding audio files.
102
103 The section on the REFERENCE(The audio file selector, audio file
104 selector) discusses this topic.
105
106
107 *para_client*
108
109 The client program to connect to para_server. paraslash commands
110 are sent to para_server and the response is dumped to STDOUT. This
111 can be used by any scripting language to produce user interfaces with
112 little programming effort.
113
114 All connections between para_server and para_client are encrypted
115 with a symmetric RC4 session key. For each user of paraslash you must
116 create a public/secret RSA key pair for authentication.
117
118
119 *para_audiod*
120
121 The local daemon that collects information from para_server.
122
123 It runs on the client side and connects to para_server. As soon as
124 para_server announces the availability of an audio stream, para_audiod
125 starts an appropriate receiver, any number of filters and a paraslash
126 writer to play the stream.
127
128 Moreover, para_audiod listens on a local socket and sends status
129 information about para_server and para_audiod to local clients on
130 request. Access via this local socket may be restricted by using Unix
131 socket credentials, if available.
132
133
134 *para_audioc*
135
136 The client program which talks to para_audiod. Used to control
137 para_audiod, to receive status info, or to grab the stream at any
138 point of the decoding process.
139
140 *para_recv*
141
142 A command line HTTP/DCCP/UDP stream grabber. The http mode is
143 compatible with arbitrary HTTP streaming sources (e.g. icecast).
144
145 *para_filter*
146
147 A filter program that reads from STDIN and writes to STDOUT.
148 Like para_recv, this is an atomic building block which can be used to
149 assemble higher-level audio receiving facilities. It combines several
150 different functionalities in one tool: decoders for multiple audio
151 formats and a number of processing filters, among these a normalizer
152 for audio volume.
153
154 *para_afh*
155
156 A small stand-alone program that prints tech info about the given
157 audio file to STDOUT. It can be instructed to print a "chunk table",
158 an array of offsets within the audio file or to write the content of
159 the audio file in complete chunks 'just in time'.
160
161 This allows third-party streaming software that is unaware of the
162 particular audio format to send complete frames in real time.
163
164 *para_write*
165
166 A modular audio stream writer. It supports a simple file writer
167 output plug-in and optional WAV/raw players for ALSA (Linux) and for
168 coreaudio (Mac OS). para_write can also be used as a stand-alone WAV
169 or raw audio player.
170
171
172 *para_gui*
173
174 Curses-based gui that presents status information obtained in a curses
175 window. Appearance can be customized via themes. para_gui provides
176 key-bindings for the most common server commands and new key-bindings
177 can be added easily.
178
179
180 *para_fade*
181
182 An (OSS-only) alarm clock and volume-fader.
183
184 -----------
185 Quick start
186 -----------
187
188 This chapter lists the REFERENCE(Requirements, necessary software)
189 that must be installed to compile the paraslash package, describes
190 how to REFERENCE(Installation, compile and install) the paraslash
191 source code and the steps that have to be performed in order to
192 REFERENCE(Quick start, set up) a typical server and client.
193
194 Requirements
195 ~~~~~~~~~~~~
196
197 In any case you'll need
198
199 - XREFERENCE(http://systemlinux.org/~maan/osl/, libosl).
200 The _object storage layer_ library is used by para_server. To
201 clone the source code repository, execute
202
203 git clone git://git.tuebingen.mpg.de/osl
204
205 - XREFERENCE(ftp://ftp.gnu.org/pub/gnu/gcc, gcc). The
206 EMPH(gnu compiler collection) is usually shipped with the
207 distro. gcc-3.3 or newer is required.
208
209 - XREFERENCE(ftp://ftp.gnu.org/pub/gnu/make, gnu make) is
210 also shipped with the disto. On BSD systems the gnu make
211 executable is often called gmake.
212
213 - XREFERENCE(ftp://ftp.gnu.org/pub/gnu/bash, bash). Some
214 scripts which run during compilation require the EMPH(Bourne
215 again shell). It is most likely already installed.
216
217 - XREFERENCE(http://www.openssl.org/, openssl). The EMPH(Secure
218 Sockets Layer) library is needed for cryptographic routines
219 on both the server and the client side. It is usually shipped
220 with the distro, but you might have to install the "development
221 package" (called libssl-dev on debian systems) as well.
222
223 - XREFERENCE(ftp://ftp.gnu.org/pub/gnu/help2man, help2man)
224 is used to create the man pages.
225
226 Optional:
227
228 - XREFERENCE(http://www.underbit.com/products/mad/, libmad).
229 To compile in MP3 support for paraslash, the development
230 package must be installed. It is called libmad0-dev on
231 debian-based systems. Note that libmad is not necessary on
232 the server side, i.e. for sending MP3 files.
233
234 - XREFERENCE(http://www.underbit.com/products/mad/,
235 libid3tag). For version-2 ID3 tag support, you'll need
236 the libid3tag development package libid3tag0-dev. Without
237 libid3tag, only version one tags are recognized.
238
239 - XREFERENCE(http://www.xiph.org/downloads/, ogg vorbis).
240 For ogg vorbis streams you'll need libogg, libvorbis,
241 libvorbisfile. The corresponding Debian packages are called
242 libogg-dev and libvorbis-dev.
243
244 - XREFERENCE(http://www.audiocoding.com/, libfaad). For aac
245 files (m4a) you'll need libfaad (libfaad-dev).
246
247 - XREFERENCE(http://www.speex.org/, speex). In order to stream
248 or decode speex files, libspeex (libspeex-dev) is required.
249
250 - XREFERENCE(ftp://ftp.alsa-project.org/pub/lib/, alsa-lib). On
251 Linux, you'll need to have ALSA's development package
252 libasound2-dev installed.
253
254 - XREFERENCE(http://downloads.xiph.org/releases/ao/,
255 libao). Needed to build the ao writer (ESD, PulseAudio,...).
256 Debian package: libao-dev.
257
258 Installation
259 ~~~~~~~~~~~~
260
261 First make sure all non-optional packages listed in the section on
262 REFERENCE(Requirements, required software) are installed on your
263 system.
264
265 You don't need everything listed there. In particular, MP3, OGG/Vorbis,
266 OGG/Speex and AAC support are all optional. The configure script will
267 detect what is installed on your system and will only try to build
268 those executables that can be built with your setup.
269
270 Note that no special decoder library (not even the MP3 decoding library
271 libmad) is needed for para_server if you only want to stream MP3 or WMA
272 files. Also, it's fine to use para_server on a box without sound card.
273
274 Next, install the paraslash package on all machines, you'd like this
275 software to run on:
276
277 (./configure && make) > /dev/null
278
279 There should be no errors but probably some warnings about missing
280 packages which usually implies that not all audio formats will be
281 supported. If headers or libs are installed at unusual locations you
282 might need to tell the configure script where to find them. Try
283
284 ./configure --help
285
286 to see a list of options. If the paraslash package was compiled
287 successfully, execute (optionally)
288
289 make test
290
291 to run the paraslash test suite. If all tests pass, execute as root
292
293 make install
294
295 to install executables under /usr/local/bin and the man pages under
296 /usr/local/man.
297
298 Configuration
299 ~~~~~~~~~~~~~
300
301 *Step 1*: Create a paraslash user
302
303 In order to control para_server at runtime you must create a paraslash
304 user. As authentication is based on the RSA crypto system you'll have
305 to create an RSA key pair. If you already have a user and an RSA key
306 pair, you may skip this step.
307
308 In this section we'll assume a typical setup: You would like to run
309 para_server on some host called server_host as user foo, and you want
310 to connect to para_server from another machine called client_host as
311 user bar.
312
313 As foo@server_host, create ~/.paraslash/server.users by typing the
314 following commands:
315
316 user=bar
317 target=~/.paraslash/server.users
318 key=~/.paraslash/key.pub.$user
319 perms=AFS_READ,AFS_WRITE,VSS_READ,VSS_WRITE
320 mkdir -p ~/.paraslash
321 echo "user $user $key $perms" >> $target
322
323 Next, change to the "bar" account on client_host and generate the
324 key pair with the commands
325
326 key=~/.paraslash/key.$LOGNAME
327 mkdir -p ~/.paraslash
328 (umask 077 && openssl genrsa -out $key 2048)
329
330 para_server only needs to know the public key of the key pair just
331 created. It can be extracted with
332
333 pubkey=~/.paraslash/key.pub.$LOGNAME
334 openssl rsa -in $key -pubout -out $pubkey
335
336 Copy the public key just created to server_host (you may skip this step
337 for a single-user setup, i.e. if foo=bar and server_host=client_host):
338
339 scp $pubkey foo@server_host:.paraslash/
340
341 Finally, tell para_client to connect to server_host:
342
343 conf=~/.paraslash/client.conf
344 echo 'hostname server_host' > $conf
345
346
347 *Step 2*: Start para_server
348
349 Before starting the server make sure you have write permissions to
350 the directory /var/paraslash that has been created during installation:
351
352 sudo chown $LOGNAME /var/paraslash
353
354 Alternatively, use the --afs_socket Option to specify a different
355 location for the AFS command socket.
356
357 For this first try, we'll use the info loglevel to make the output
358 of para_server more verbose.
359
360 para_server -l info
361
362 Now you can use para_client to connect to the server and issue
363 commands. Open a new shell as bar@client_host and try
364
365 para_client help
366 para_client si
367
368 to retrieve the list of available commands and some server info.
369 Don't proceed if this doesn't work.
370
371 *Step 3*: Create and populate the database
372
373 An empty database is created with
374
375 para_client init
376
377 This initializes a couple of empty tables under
378 ~/.paraslash/afs_database-0.4. You normally don't need to look at these
379 tables, but it's good to know that you can start from scratch with
380
381 rm -rf ~/.paraslash/afs_database-0.4
382
383 in case something went wrong.
384
385 Next, you need to add some audio files to that database so that
386 para_server knows about them. Choose an absolute path to a directory
387 containing some audio files and add them to the audio file table:
388
389 para_client add /my/mp3/dir
390
391 This might take a while, so it is a good idea to start with a directory
392 containing not too many files. Note that the table only contains data
393 about the audio files found, not the files themselves.
394
395 You may print the list of all known audio files with
396
397 para_client ls
398
399 *Step 4*: Configure para_audiod
400
401 para_audiod needs to create a "well-known" socket for the clients to
402 connect to. The default path for this socket is
403
404 /var/paraslash/audiod_socket.$HOSTNAME
405
406 In order to make this directory writable for para_audiod, execute
407 as bar@client_host
408
409 sudo chown $LOGNAME /var/paraslash
410
411
412 We will also have to tell para_audiod that it should receive the
413 audio stream from server_host:
414
415 para_audiod -l info -r 'mp3:http -i server_host'
416
417 You should now be able to listen to the audio stream once para_server
418 starts streaming. To activate streaming, execute
419
420 para_client play
421
422 Since no playlist has been specified yet, the "dummy" mode which
423 selects all known audio files is activated automatically. See the
424 section on the REFERENCE(The audio file selector, audio file selector)
425 for how to use playlists and moods to specify which files should be
426 streamed in which order.
427
428 *Troubleshooting*
429
430 It did not work? To find out why, try to receive, decode and play the
431 stream manually using para_recv, para_filter and para_write as follows.
432
433 For simplicity we assume that you're running Linux/ALSA and that only
434 MP3 files have been added to the database.
435
436 para_recv -r 'http -i server_host' > file.mp3
437 # (interrupt with CTRL+C after a few seconds)
438 ls -l file.mp3 # should not be empty
439 para_filter -f mp3dec -f wav < file.mp3 > file.wav
440 ls -l file.wav # should be much bigger than file.mp3
441 para_write -w alsa < file.wav
442
443 Double check what is logged by para_server and use the --loglevel
444 option of para_recv, para_filter and para_write to increase verbosity.
445
446 ---------------
447 User management
448 ---------------
449
450 para_server uses a challenge-response mechanism to authenticate
451 requests from incoming connections, similar to ssh's public key
452 authentication method. Authenticated connections are encrypted using
453 the RC4 stream cipher.
454
455 In this chapter we briefly describe RSA and RC4 and sketch the
456 REFERENCE(Client-server authentication, authentication handshake)
457 between para_client and para_server. User management is discussed
458 in the section on REFERENCE(The user_list file, the user_list file).
459 These sections are all about communication between the client and the
460 server. Connecting para_audiod is a different matter and is described
461 in a REFERENCE(Connecting para_audiod, separate section).
462
463
464
465 RSA and RC4
466 ~~~~~~~~~~~
467
468 RSA is an asymmetric block cipher which is used in many applications,
469 including ssh and gpg. An RSA key consists in fact of two keys,
470 called the public key and the private key. A message can be encrypted
471 with either key and only the counterpart of that key can decrypt
472 the message. While RSA can be used for both signing and encrypting
473 a message, paraslash only uses RSA only for the latter purpose. The
474 RSA public key encryption and signatures algorithms are defined in
475 detail in RFC 2437.
476
477 RC4 is a stream cipher, i.e. the input is XORed with a pseudo-random
478 key stream to produce the output. Decryption uses the same function
479 calls as encryption. While RC4 supports variable key lengths,
480 paraslash uses a fixed length of 256 bits, which is considered a
481 strong encryption by today's standards. Since the same key must never
482 be used twice, a different, randomly-generated key is used for every
483 new connection.
484
485 Client-server authentication
486 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
487
488 The authentication handshake between para_client and para_server goes
489 as follows:
490
491 - para_client connects to para_server and sends an
492 authentication request for a user. It does so by connecting
493 to para_server, TCP 2990, the control port of para_server.
494
495 - para_server accepts the connection and forks a child process
496 which is supposed to handle the connection. The parent process
497 keeps listening on the control port while the child process
498 (also called para_server below) continues as follows.
499
500 - para_server loads the RSA public key of that user, fills a
501 fixed-length buffer with random bytes, encrypts that buffer
502 using the public key and sends the encrypted buffer to the
503 client. The first part of the buffer is the challenge which
504 is used for authentication while the second part is the RC4
505 session key.
506
507 - para_client receives the encrypted buffer and decrypts it
508 using the user's private key, thereby obtaining the challenge
509 buffer and the session key. It sends the SHA1 hash value of
510 the challenge back to para_server and stores the session key
511 for further use.
512
513 - para_server also computes the SHA1 hash of the challenge
514 and compares it against what was sent back by the client.
515
516 - If the two hashes do not match, the authentication has
517 failed and para_server closes the connection.
518
519 - Otherwise the user is considered authenticated and the client
520 is allowed to proceed by sending a command to be executed. From
521 this point on the communication is encrypted using the RC4
522 stream cipher with the session key known to both peers.
523
524 paraslash relies on the quality of openssl's cryptographically strong
525 pseudo-random bytes, on the security of the implementation of the
526 openssl RSA and RC4 crypto routines and on the infeasibility to invert
527 the SHA1 function.
528
529 Neither para_server or para_client create RSA keys on their own. This
530 has to be done once for each user as sketched in REFERENCE(Quick start,
531 Quick start) and discussed in more detail REFERENCE(The user_list
532 file, below).
533
534 The user_list file
535 ~~~~~~~~~~~~~~~~~~
536
537 At startup para_server reads the user list file which must contain
538 one line per user. The default location of the user list file may be
539 changed with the --user_list option.
540
541 There should be at least one user in this file. Each user must have
542 an RSA key pair. The public part of the key is needed by para_server
543 while the private key is needed by para_client. Each line of the
544 user list file must be of the form
545
546 user <username> <key> <perms>
547
548 where _username_ is an arbitrary string (usually the user's login
549 name), _key_ is the full path to that user's public RSA key, and
550 _perms_ is a comma-separated list of zero or more of the following
551 permission bits:
552
553 +---------------------------------------------------------+
554 | AFS_READ | read the contents of the databases |
555 +-----------+---------------------------------------------+
556 | AFS_WRITE | change database contents |
557 +-----------+---------------------------------------------+
558 | VSS_READ | obtain information about the current stream |
559 +-----------+---------------------------------------------+
560 | VSS_WRITE | change the current stream |
561 +---------------------------------------------------------+
562
563 The permission bits specify which commands the user is allowed to
564 execute. The output of
565
566 para_client help
567
568 contains in the third column the permissions needed to execute the
569 command.
570
571 A new RSA key can be created with
572
573 openssl genrsa -out <private_key> 2048
574
575 and the public part may be extracted with
576
577 openssl rsa -in <private_key> -pubout -out <public_key>
578
579 Note that para_server refuses to use a key if it is shorter than 2048
580 bits. In particular, the RSA keys of paraslash 0.3.x will not work
581 with version 0.4.x. Moreover, para_client refuses to use a (private)
582 key which is world-readable.
583
584 It is possible to make para_server reread the user_list file by
585 executing the paraslash "hup" command or by sending SIGHUP to the
586 PID of para_server.
587
588
589 Connecting para_audiod
590 ~~~~~~~~~~~~~~~~~~~~~~
591
592 para_audiod listens on a Unix domain socket. Those sockets are
593 for local communication only, so only local users can connect to
594 para_audiod. The default is to let any user connect but this can be
595 restricted on platforms that support UNIX socket credentials which
596 allow para_audiod to obtain the Unix credentials of the connecting
597 process.
598
599 Use para_audiod's --user_allow option to allow connections only for
600 a limited set of users.
601
602 -----------------------
603 The audio file selector
604 -----------------------
605
606 paraslash comes with a sophisticated audio file selector (AFS),
607 whose main task is to determine which file to stream next, based on
608 information on the audio files stored in a database. It communicates
609 also with para_client whenever an AFS command is executed, for example
610 to answer a database query.
611
612 Besides the traditional playlists, AFS supports audio file selection
613 based on _moods_ which act as a filter that limits the set of all
614 known audio files to those which satisfy certain criteria. It also
615 maintains tables containing images (e.g. album cover art) and lyrics
616 that can be associated with one or more audio files.
617
618 AFS uses libosl, the object storage layer, as the backend library
619 for storing information on audio files, playlists, etc. This library
620 offers functionality similar to a relational database, but is much
621 more lightweight than a full database backend.
622
623 In this chapter we sketch the setup of the REFERENCE(The AFS process,
624 AFS process) during server startup and proceed with the description
625 of the REFERENCE(Database layout, layout) of the various database
626 tables. The section on REFERENCE(Playlists and moods, playlists
627 and moods) explains these two audio file selection mechanisms
628 in detail and contains pratical examples. The way REFERENCE(File
629 renames and content changes, file renames and content changes) are
630 detected is discussed briefly before the REFERENCE(Troubleshooting,
631 Troubleshooting) section which concludes the chapter.
632
633 The AFS process
634 ~~~~~~~~~~~~~~~
635
636 On startup, para_server forks to create the AFS process which opens
637 the OSL database tables. The server process communicates with the
638 AFS process via pipes and shared memory. Usually, the AFS process
639 awakes only briefly whenever the current audio file changes. The AFS
640 process determines the next audio file, opens it, verifies it has
641 not been changed since it was added to the database and passes the
642 open file descriptor to the server process, along with audio file
643 meta-data such as file name, duration, audio format and so on. The
644 server process then starts to stream the audio file.
645
646 The AFS process also accepts connections from local clients via
647 a well-known socket. However, only child processes of para_server
648 may connect through this socket. All server commands that have the
649 AFS_READ or AFS_WRITE permission bits use this mechanism to query or
650 change the database.
651
652 Database layout
653 ~~~~~~~~~~~~~~~
654
655 *The audio file table*
656
657 This is the most important and usually also the largest table of the
658 AFS database. It contains the information needed to stream each audio
659 file. In particular the following data is stored for each audio file.
660
661 - SHA1 hash value of the audio file contents. This is computed
662 once when the file is added to the database. Whenever AFS
663 selects this audio file for streaming the hash value is
664 recomputed and checked against the value stored in the
665 database to detect content changes.
666
667 - The time when this audio file was last played.
668
669 - The number of times the file has been played so far.
670
671 - The attribute bitmask.
672
673 - The image id which describes the image associated with this
674 audio file.
675
676 - The lyrics id which describes the lyrics associated with
677 this audio file.
678
679 - The audio format id (MP3, OGG, ...).
680
681 - An amplification value that can be used by the amplification
682 filter to pre-amplify the decoded audio stream.
683
684 - The chunk table. It describes the location and the timing
685 of the building blocks of the audio file. This is used by
686 para_server to send chunks of the file at appropriate times.
687
688 - The duration of the audio file.
689
690 - Tag information contained in the audio file (ID3 tags,
691 Vorbis comments, ...).
692
693 - The number of channels
694
695 - The encoding bitrate.
696
697 - The sampling frequency.
698
699 To add or refresh the data contained in the audio file table, the _add_
700 command is used. It takes the full path of either an audio file or a
701 directory. In the latter case, the directory is traversed recursively
702 and all files which are recognized as valid audio files are added to
703 the database.
704
705 *The attribute table*
706
707 The attribute table contains two columns, _name_ and _bitnum_. An
708 attribute is simply a name for a certain bit number in the attribute
709 bitmask of the audio file table.
710
711 Each of the 64 bits of the attribute bitmask can be set for each
712 audio file individually. Hence up to 64 different attributes may be
713 defined. For example, "pop", "rock", "blues", "jazz", "instrumental",
714 "german_lyrics", "speech", whatever. You are free to choose as
715 many attributes as you like and there are no naming restrictions
716 for attributes.
717
718 A new attribute "test" is created by
719
720 para_client addatt test
721 and
722 para_client lsatt
723
724 lists all available attributes. You can set the "test" attribute for
725 an audio file by executing
726
727 para_client setatt test+ /path/to/the/audio/file
728
729 Similarly, the "test" bit can be removed from an audio file with
730
731 para_client setatt test- /path/to/the/audio/file
732
733 Instead of a path you may use a shell wildcard pattern. The attribute
734 is applied to all audio files matching that pattern:
735
736 para_client setatt test+ '/test/directory/*'
737
738 The command
739
740 para_client -- ls -lv
741
742 gives you a verbose listing of your audio files also showing which
743 attributes are set.
744
745 In case you wonder why the double-dash in the above command is needed:
746 It tells para_client to not interpret the options after the dashes. If
747 you find this annoying, just say
748
749 alias para='para_client --'
750
751 and be happy. In what follows we shall use this alias.
752
753 The "test" attribute can be dropped from the database with
754
755 para rmatt test
756
757 Read the output of
758
759 para help ls
760 para help setatt
761
762 for more information and a complete list of command line options to
763 these commands.
764
765 *Blob tables*
766
767 The image, lyrics, moods and playlists tables are all blob tables.
768 Blob tables consist of three columns each: The identifier which is
769 a positive non-negative number that is auto-incremented, the name
770 (an arbitrary string) and the content (the blob).
771
772 All blob tables support the same set of actions: cat, ls, mv, rm
773 and add. Of course, _add_ is used for adding new blobs to the table
774 while the other actions have the same meaning as the corresponding
775 Unix commands. The paraslash commands to perform these actions are
776 constructed as the concatenation of the table name and the action. For
777 example addimg, catimg, lsimg, mvimg, rmimg are the commands that
778 manipulate or query the image table.
779
780 The add variant of these commands is special as these commands read
781 the blob contents from stdin. To add an image to the image table the
782 command
783
784 para addimg image_name < file.jpg
785
786 can be used.
787
788 Note that the images and lyrics are not interpreted at all, and also
789 the playlist and the mood blobs are only investigated when the mood
790 or playlist is activated by using the select command.
791
792 *The score table*
793
794 Unlike all other tables the contents of the score table remain in
795 memory and are never stored on disk. The score table contains two
796 columns: The SHA1 hash value (of an audio file) and its current
797 score.
798
799 However, only those files which are admissible for the current mood
800 or playlist are contained in the score table. The audio file selector
801 always chooses the row with the highest score as the file to stream
802 next. While doing so, it computes the new score and updates the
803 last_played and the num_played fields in the audio file table.
804
805 The score table is recomputed by the select command which loads a
806 new mood or playlist.
807
808 Playlists and moods
809 ~~~~~~~~~~~~~~~~~~~
810
811 Playlists and moods offer two different ways of specifying the set of
812 admissible files. A playlist in itself describes a set of admissible
813 files. A mood, in contrast, describes the set of admissible files in
814 terms of attributes and other type of information available in the
815 audio file table. As an example, a mood can define a filename pattern,
816 which is then matched against the names of audio files in the table.
817
818 Selecting a mood or playlist means the generation of a ranking
819 (a score table) for the set of admissible files. Audio files are
820 then selected on a highest-score-first basis. The score table is
821 recomputed at the moment the mood or playlist is selected.
822
823 *Playlists*
824
825 Playlists are accommodated in the playlist table of the afs database,
826 using the aforementioned blob format for tables. A new filelist is
827 created using the addpl command, by specifying the full (absolute)
828 paths of all desired audio files, separated by newlines. For example
829
830 find /my/mp3/dir -name "*.mp3" | para addpl my_playlist
831
832 If _my_playlist_ already exists it is overwritten. To activate the
833 new playlist, execute
834
835 para select p/my_playlist
836
837 The audio file selector will assign scores to each entry of the list,
838 in descending order so that files will be selected in order. If a
839 file could not be opened for streaming, its entry is removed from
840 the score table (but not from the playlist).
841
842 *Moods*
843
844 A mood consists of a unique name and its *mood definition*, which is
845 a set of *mood lines* containing expressions in terms of attributes
846 and other data contained in the database.
847
848 At any time, at most one mood can be *active* which means that
849 para_server is going to select only files from that subset of
850 admissible files.
851
852 So in order to create a mood definition one has to write a set of
853 mood lines. Mood lines come in three flavours: Accept lines, deny
854 lines and score lines.
855
856 The general syntax of the three types of mood lines is
857
858
859 accept [with score <score>] [if] [not] <mood_method> [options]
860 deny [with score <score>] [if] [not] <mood_method> [options]
861 score <score> [if] [not] <mood_method> [options]
862
863
864 Here <score> is either an integer or the string "random" which assigns
865 a random score to all matching files. The score value changes the
866 order in which admissible files are going to be selected, but is of
867 minor importance for this introduction.
868
869 So we concentrate on the first two forms, i.e. accept and deny
870 lines. As usual, everything in square brackets is optional, i.e.
871 accept/deny lines take the following form when ignoring scores:
872
873 accept [if] [not] <mood_method> [options]
874
875 and analogously for the deny case. The "if" keyword is only syntactic
876 sugar and has no function. The "not" keyword just inverts the result,
877 so the essence of a mood line is the mood method part and the options
878 following thereafter.
879
880 A *mood method* is realized as a function which takes an audio file
881 and computes a number from the data contained in the database.
882 If this number is non-negative, we say the file *matches* the mood
883 method. The file matches the full mood line if it either
884
885 - matches the mood method and the "not" keyword is not given,
886 or
887 - does not match the mood method, but the "not" keyword is given.
888
889 The set of admissible files for the whole mood is now defined as those
890 files which match at least one accept mood line, but no deny mood line.
891 More formally, an audio file F is admissible if and only if
892
893 (F ~ AL1 or F ~ AL2...) and not (F ~ DL1 or F ~ DN2 ...)
894
895 where AL1, AL2... are the accept lines, DL1, DL2... are the deny
896 lines and "~" means "matches".
897
898 The cases where no mood lines of accept/deny type are defined need
899 special treatment:
900
901 - Neither accept nor deny lines: This treats all files as
902 admissible (in fact, that is the definition of the dummy mood
903 which is activated automatically if no moods are available).
904
905 - Only accept lines: A file is admissible iff it matches at
906 least one accept line:
907
908 F ~ AL1 or F ~ AL2 or ...
909
910 - Only deny lines: A file is admissible iff it matches no
911 deny line:
912
913 not (F ~ DL1 or F ~ DN2 ...)
914
915
916
917 *List of mood_methods*
918
919 no_attributes_set
920
921 Takes no arguments and matches an audio file if and only if no
922 attributes are set.
923
924 is_set <attribute_name>
925
926 Takes the name of an attribute and matches iff that attribute is set.
927
928 path_matches <pattern>
929
930 Takes a filename pattern and matches iff the path of the audio file
931 matches the pattern.
932
933 artist_matches <pattern>
934 album_matches <pattern>
935 title_matches <pattern>
936 comment_matches <pattern>
937
938 Takes an extended regular expression and matches iff the text of the
939 corresponding tag of the audio file matches the pattern. If the tag
940 is not set, the empty string is matched against the pattern.
941
942 year ~ <num>
943 bitrate ~ <num>
944 frequency ~ <num>
945 channels ~ <num>
946 num_played ~ <num>
947
948 Takes a comparator ~ of the set {<, =, <=, >, >=, !=} and a number
949 <num>. Matches an audio file iff the condition <val> ~ <num> is
950 satisfied where val is the corresponding value of the audio file
951 (value of the year tag, bitrate in kbit/s, frequency in Hz, channel
952 count, play count).
953
954 The year tag is special as its value is undefined if the audio file
955 has no year tag or the content of the year tag is not a number. Such
956 audio files never match. Another difference is the special treatment
957 if the year tag is a two-digit number. In this case either 1900 or
958 2000 are added to the tag value depending on whether the number is
959 greater than 2000 plus the current year.
960
961
962 *Mood usage*
963
964 To create a new mood called "my_mood", write its definition into
965 some temporary file, say "tmpfile", and add it to the mood table
966 by executing
967
968 para addmood my_mood < tmpfile
969
970 If the mood definition is really short, you may just pipe it to the
971 client instead of using temporary files. Like this:
972
973 echo "$MOOD_DEFINITION" | para addmood my_mood
974
975 There is no need to keep the temporary file since you can always use
976 the catmood command to get it back:
977
978 para catmood my_mood
979
980 A mood can be activated by executing
981
982 para select m/my_mood
983
984 Once active, the list of admissible files is shown by the ls command
985 if the "-a" switch is given:
986
987 para ls -a
988
989
990 *Example mood definition*
991
992 Suppose you have defined attributes "punk" and "rock" and want to define
993 a mood containing only Punk-Rock songs. That is, an audio file should be
994 admissible if and only if both attributes are set. Since
995
996 punk and rock
997
998 is obviously the same as
999
1000 not (not punk or not rock)
1001
1002 (de Morgan's rule), a mood definition that selects only Punk-Rock
1003 songs is
1004
1005 deny if not is_set punk
1006 deny if not is_set rock
1007
1008
1009
1010 File renames and content changes
1011 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1012
1013 Since the audio file selector knows the SHA1 of each audio file that
1014 has been added to the afs database, it recognizes if the content of
1015 a file has changed, e.g. because an ID3 tag was added or modified.
1016 Also, if a file has been renamed or moved to a different location,
1017 afs will detect that an entry with the same hash value already exists
1018 in the audio file table.
1019
1020 In both cases it is enough to just re-add the new file. In the
1021 first case (file content changed), the audio table is updated, while
1022 metadata such as the num_played and last_played fields, as well as
1023 the attributes, remain unchanged. In the other case, when the file
1024 is moved or renamed, only the path information is updated, all other
1025 data remains as before.
1026
1027 It is possible to change the behaviour of the add command by using the
1028 "-l" (lazy add) or the "-f" (force add) option.
1029
1030 Troubleshooting
1031 ~~~~~~~~~~~~~~~
1032
1033 Use the debug loglevel (option -l debug for most commands) to show
1034 debugging info. Almost all paraslash executables have a brief online
1035 help which is displayed by using the -h switch. The --detailed-help
1036 option prints the full help text.
1037
1038 If para_server crashed or was killed by SIGKILL (signal 9), it
1039 may refuse to start again because of "dirty osl tables". In this
1040 case you'll have to run the oslfsck program of libosl to fix your
1041 database. It might be necessary to use --force (even if your name
1042 isn't Luke). However, make sure para_server isn't running before
1043 executing oslfsck --force.
1044
1045 If you don't mind to recreate your database you can start
1046 from scratch by removing the entire database directory, i.e.
1047
1048 rm -rf ~/.paraslash/afs_database-0.4
1049
1050 Be aware that this removes all attribute definitions, all playlists
1051 and all mood definitions and requires to re-initialize the tables.
1052
1053 Although oslfsck fixes inconsistencies in database tables it doesn't
1054 care about the table contents. To check for invalid table contents, use
1055
1056 para_client check
1057
1058 This prints out references to missing audio files as well as invalid
1059 playlists and mood definitions.
1060
1061 ---------------------------------------
1062 Audio formats and audio format handlers
1063 ---------------------------------------
1064
1065 Audio formats
1066 ~~~~~~~~~~~~~
1067
1068 The following audio formats are supported by paraslash:
1069
1070 *MP3*
1071
1072 Mp3, MPEG-1 Audio Layer 3, is a common audio format for audio storage,
1073 designed as part of its MPEG-1 standard. An MP3 file is made up of
1074 multiple MP3 frames, which consist of a header and a data block. The
1075 size of an MP3 frame depends on the bit rate and on the number
1076 of channels. For a typical CD-audio file (sample rate of 44.1 kHz
1077 stereo), encoded with a bit rate of 128 kbit, an MP3 frame is about
1078 400 bytes large.
1079
1080 *OGG/Vorbis*
1081
1082 OGG is a standardized audio container format, while Vorbis is an
1083 open source codec for lossy audio compression. Since Vorbis is most
1084 commonly made available via the OGG container format, it is often
1085 referred to as OGG/Vorbis. The OGG container format divides data into
1086 chunks called OGG pages. A typical OGG page is about 4KB large. The
1087 Vorbis codec creates variable-bitrate (VBR) data, where the bitrate
1088 may vary considerably.
1089
1090 *OGG/Speex*
1091
1092 Speex is an open-source speech codec that is based on CELP (Code
1093 Excited Linear Prediction) coding. It is designed for voice
1094 over IP applications, has modest complexity and a small memory
1095 footprint. Wideband and narrowband (telephone quality) speech are
1096 supported. As for Vorbis audio, Speex bit-streams are often stored
1097 in OGG files.
1098
1099 *AAC*
1100
1101 Advanced Audio Coding (AAC) is a standardized, lossy compression
1102 and encoding scheme for digital audio which is the default audio
1103 format for Apple's iPhone, iPod, iTunes. Usually MPEG-4 is used as
1104 the container format and audio files encoded with AAC have the .m4a
1105 extension. A typical AAC frame is about 700 bytes large.
1106
1107 *WMA*
1108
1109 Windows Media Audio (WMA) is an audio data compression technology
1110 developed by Microsoft. A WMA file is usually encapsulated in the
1111 Advanced Systems Format (ASF) container format, which also specifies
1112 how meta data about the file is to be encoded. The bit stream of WMA
1113 is composed of superframes, each containing one or more frames of
1114 2048 samples. For 16 bit stereo a WMA superframe is about 8K large.
1115
1116 Meta data
1117 ~~~~~~~~~
1118
1119 Unfortunately, each audio format has its own conventions how meta
1120 data is added as tags to the audio file.
1121
1122 For MP3 files, ID3, version 1 and 2 are widely used. ID3 version 1
1123 is rather simple but also very limited as it supports only artist,
1124 title, album, year and comment tags. Each of these can only be at most
1125 32 characters long. ID3, version 2 is much more flexible but requires
1126 a separate library being installed for paraslash to support it.
1127
1128 Ogg vorbis files contain meta data as Vorbis comments, which are
1129 typically implemented as strings of the form "[TAG]=[VALUE]". Unlike
1130 ID3 version 1 tags, one may use whichever tags are appropriate for
1131 the content.
1132
1133 AAC files usually use the MPEG-4 container format for storing meta
1134 data while WMA files wrap meta data as special objects within the
1135 ASF container format.
1136
1137 paraslash only tracks the most common tags that are supported by
1138 all tag variants: artist, title, year, album, comment. When a file
1139 is added to the AFS database, the meta data of the file is extracted
1140 and stored in the audio file table.
1141
1142 Chunks and chunk tables
1143 ~~~~~~~~~~~~~~~~~~~~~~~
1144
1145 paraslash uses the word "chunk" as common term for the building blocks
1146 of an audio file. For MP3 files, a chunk is the same as an MP3 frame,
1147 while for OGG files a chunk is an OGG page, etc. Therefore the chunk
1148 size varies considerably between audio formats, from a few hundred
1149 bytes (MP3) up to 8K (WMA).
1150
1151 The chunk table contains the offsets within the audio file that
1152 correspond to the chunk boundaries of the file. Like the meta data,
1153 the chunk table is computed and stored in the database whenever an
1154 audio file is added.
1155
1156 The paraslash senders (see below) always send complete chunks. The
1157 granularity for seeking is therefore determined by the chunk size.
1158
1159 Audio format handlers
1160 ~~~~~~~~~~~~~~~~~~~~~
1161
1162 For each audio format paraslash contains an audio format handler whose
1163 first task is to tell whether a given file is a valid audio file of
1164 this type. If so, the audio file handler extracts some technical data
1165 (duration, sampling rate, number of channels etc.), computes the
1166 chunk table and reads the meta data.
1167
1168 The audio format handler code is linked into para_server and executed
1169 via the _add_ command. The same code is also available as a stand-alone
1170 tool, para_afh, which can be used to print the technical data, the
1171 chunk table and the meta data of a file. Furthermore, one can use
1172 para_afh to cut an audio file, i.e. to select some of its chunks to
1173 produce a new file containing only these chunks.
1174
1175 ----------
1176 Networking
1177 ----------
1178
1179 Paraslash uses different network connections for control and data.
1180 para_client communicates with para_server over a dedicated TCP control
1181 connection. To transport audio data, separate data connections are
1182 used. For these data connections, a variety of transports (UDP, DCCP,
1183 HTTP) can be chosen.
1184
1185 The chapter starts with the REFERENCE(The paraslash control
1186 service, control service), followed by a section on the various
1187 REFERENCE(Streaming protocols, streaming protocols) in which the data
1188 connections are described. The way audio file headers are embedded into
1189 the stream is discussed REFERENCE(Streams with headers and headerless
1190 streams, briefly) before the REFERENCE(Networking examples, example
1191 section) which illustrates typical commands for real-life scenarios.
1192
1193 Both IPv4 and IPv6 are supported.
1194
1195 The paraslash control service
1196 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1197
1198 para_server is controlled at runtime via the paraslash control
1199 connection. This connection is used for server commands (play, stop,
1200 ...) as well as for afs commands (ls, select, ...).
1201
1202 The server listens on a TCP port and accepts connections from clients
1203 that connect the open port. Each connection causes the server to fork
1204 off a client process which inherits the connection and deals with that
1205 client only. In this classical accept/fork approach the server process
1206 is unaffected if the child dies or goes crazy for whatever reason. In
1207 fact, the child process can not change address space of server process.
1208
1209 The section on REFERENCE(Client-server authentication, client-server
1210 authentication) above described the early connection establishment
1211 from the crypto point of view. Here it is described what happens
1212 after the connection (including crypto setup) has been established.
1213 There are four processes involved during command dispatch as sketched
1214 in the following diagram.
1215
1216 <<
1217 <pre>
1218 server_host client_host
1219 ~~~~~~~~~~~ ~~~~~~~~~~~
1220
1221 +-----------+ connect +-----------+
1222 |para_server|<------------------------------ |para_client|
1223 +-----------+ +-----------+
1224 | ^
1225 | fork +---+ |
1226 +----------> |AFS| |
1227 | +---+ |
1228 | ^ |
1229 | | |
1230 | | connect (cookie) |
1231 | | |
1232 | | |
1233 | fork +-----+ inherited connection |
1234 +---------->|child|<--------------------------+
1235 +-----+
1236 </pre>
1237 >>
1238
1239 Note that the child process is not a child of the afs process,
1240 so communication of these two processes has to happen via local
1241 sockets. In order to avoid abuse of the local socket by unrelated
1242 processes, a magic cookie is created once at server startup time just
1243 before the server process forks off the AFS process. This cookie is
1244 known to the server, AFS and the child, but not to unrelated processes.
1245
1246 There are two different kinds of commands: First there are commands
1247 that cause the server to respond with some answer such as the list
1248 of all audio files. All but the addblob commands (addimg, addlyr,
1249 addpl, addmood) are of this kind. The addblob commands add contents
1250 to the database, so they need to transfer data the other way round,
1251 from the client to the server.
1252
1253 There is no knowledge about the server commands built into para_client,
1254 so it does not know about addblob commands. Instead, it inspects the
1255 first data package sent by the server for a magic string. If this
1256 string was found, it sends STDIN to the server, otherwise it dumps
1257 data from the server to STDOUT.
1258
1259 Streaming protocols
1260 ~~~~~~~~~~~~~~~~~~~
1261
1262 A network (audio) stream usually consists of one streaming source,
1263 the _sender_, and one or more _receivers_ which read data over the
1264 network from the streaming source.
1265
1266 Senders are thus part of para_server while receivers are part of
1267 para_audiod. Moreover, there is the stand-alone tool para_recv which
1268 can be used to manually download a stream, either from para_server
1269 or from a web-based audio streaming service.
1270
1271 The following three streaming protocols are supported by paraslash:
1272
1273 - HTTP. Recommended for public streams that can be played by
1274 any player like mpg123, xmms, itunes, winamp, etc. The HTTP
1275 sender is supported on all operating systems and all platforms.
1276
1277 - DCCP. Recommended for LAN streaming. DCCP is currently
1278 available only for Linux.
1279
1280 - UDP. Recommended for multicast LAN streaming.
1281
1282 See the Appendix on REFERENCE(Network protocols, network protocols)
1283 for brief descriptions of the various protocols relevant for network
1284 audio streaming with paraslash.
1285
1286 It is possible to activate more than one sender simultaneously.
1287 Senders can be controlled at run time and via config file and command
1288 line options.
1289
1290 Note that audio connections are _not_ encrypted. Transport or Internet
1291 layer encryption should be used if encrypted data connections are
1292 needed.
1293
1294 Since DCCP and TCP are both connection-oriented protocols, connection
1295 establishment/teardown and access control are very similar between
1296 these two streaming protocols. UDP is the most lightweight option,
1297 since in contrast to TCP/DCCP it is connectionless. It is also the
1298 only protocol supporting IP multicast.
1299
1300 The HTTP and the DCCP sender listen on a (TCP/DCCP) port waiting for
1301 clients to connect and establish a connection via some protocol-defined
1302 handshake mechanism. Both senders maintain two linked lists each:
1303 The list of all clients which are currently connected, and the list
1304 of access control entries which determines who is allowed to connect.
1305 IP-based access control may be configured through config file and
1306 command line options and via the "allow" and "deny" sender subcommands.
1307
1308 Upon receiving a GET request from the client, the HTTP sender sends
1309 back a status line and a message. The body of this message is the
1310 audio stream. This is common practice and is supported by many popular
1311 clients which can thus be used to play a stream offered by para_server.
1312 For DCCP things are a bit simpler: No messages are exchanged between
1313 the receiver and sender. The client simply connects and the sender
1314 starts to stream.
1315
1316 DCCP is an experimental protocol which offers a number of new features
1317 not available for TCP. Both ends can negotiate these features using
1318 a built-in negotiation mechanism. In contrast to TCP/HTTP, DCCP is
1319 datagram-based (no retransmissions) and thus should not be used over
1320 lossy media (e.g. WiFi networks). One useful feature offered by DCCP
1321 is access to a variety of different congestion-control mechanisms
1322 called CCIDs. Two different CCIDs are available per default on Linux:
1323
1324
1325 - _CCID 2_. A Congestion Control mechanism similar to that
1326 of TCP. The sender maintains a congestion window and halves
1327 this window in response to congestion.
1328
1329
1330 - _CCID-3_. Designed to be fair when competing for bandwidth.
1331 It has lower variation of throughput over time compared with
1332 TCP, which makes it suitable for streaming media.
1333
1334 Unlike the HTTP and DCCP senders, the UDP sender maintains only a
1335 single list, the _target list_. This list describes the set of clients
1336 to which the stream is sent. There is no list for access control and
1337 no "allow" and "deny" commands for the UDP sender. Instead, the "add"
1338 and "delete" commands can be used to modify the target list.
1339
1340 Since both UDP and DCCP offer an unreliable datagram-based transport,
1341 additional measures are necessary to guard against disruptions over
1342 networks that are lossy or which may be subject to interference (as
1343 is for instance the case with WiFi). Paraslash uses FEC (Forward
1344 Error Correction) to guard against packet losses and reordering. The
1345 stream is FEC-encoded before it is sent through the UDP socket and
1346 must be decoded accordingly on the receiver side.
1347
1348 The packet size and the amount of redundancy introduced by FEC can
1349 be configured via the FEC parameters which are dictated by server
1350 and may also be configured through the "sender" command. The FEC
1351 parameters are encoded in the header of each network packet, so no
1352 configuration is necessary on the receiver side. See the section on
1353 REFERENCE(Forward error correction, FEC) below.
1354
1355 Streams with headers and headerless streams
1356 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1357
1358 For OGG/Vorbis, OGG/Speex and wma streams, some of the information
1359 needed to decode the stream is only contained in the audio file
1360 header of the container format but not in each data chunk. Clients
1361 must be able to obtain this information in case streaming starts in
1362 the middle of the file or if para_audiod is started while para_server
1363 is already sending a stream.
1364
1365 This is accomplished in different ways, depending on the streaming
1366 protocol. For connection-oriented streams (HTTP, DCCP) the audio file
1367 header is sent prior to audio file data. This technique however does
1368 not work for the connectionless UDP transport. Hence the audio file
1369 header is periodically being embedded into the UDP audio data stream.
1370 By default, the header is resent after five seconds. The receiver has
1371 to wait until the next header arrives before it can start decoding
1372 the stream.
1373
1374 Examples
1375 ~~~~~~~~
1376
1377 The sender command of para_server allows to (de-)activate senders
1378 and to change the access permissions senders at runtime. The "si"
1379 (server info) command is used to list the streaming options of the
1380 currently running server as well as the various sender access lists.
1381
1382 -> Show client/target/access lists:
1383
1384 para_client si
1385
1386 -> Obtain general help for the sender command:
1387
1388 para_client help sender
1389
1390 -> Get help for a specific sender (contains further examples):
1391
1392 s=http # or dccp or udp
1393 para_client sender $s help
1394
1395 By default para_server activates both the HTTP and th DCCP sender on
1396 startup. This can be changed via command line options or para_server's
1397 config file.
1398
1399 -> List config file options for senders:
1400
1401 para_server -h
1402
1403 All senders share the "on" and "off" commands, so senders may be
1404 activated and deactivated independently of each other.
1405
1406 -> Switch off the http sender:
1407
1408 para_client sender http off
1409
1410 -> Receive a DCCP stream using CCID2 and write the output into a file:
1411
1412 host=foo.org; ccid=2; filename=bar
1413 para_recv --receiver "dccp --host $host --ccid $ccid" > $filename
1414
1415 Note the quotes around the arguments for the dccp receiver. Each
1416 receiver has its own set of command line options and its own command
1417 line parser, so arguments for the dccp receiver must be protected
1418 from being interpreted by para_recv.
1419
1420 -> Start UDP multicast, using the default multicast address:
1421
1422 para_client sender udp add 224.0.1.38
1423
1424 -> Receive FEC-encoded multicast stream and write the output into a file:
1425
1426 filename=foo
1427 para_recv -r udp > $filename
1428
1429 -> Add an UDP unicast for a client to the target list of the UDP sender:
1430
1431 t=client.foo.org
1432 para_client sender udp add $t
1433
1434 -> Receive this (FEC-encoded) unicast stream:
1435
1436 filename=foo
1437 para_recv -r 'udp -i 0.0.0.0' > $filename
1438
1439 -> Create a minimal config for para_audiod for HTTP streams:
1440
1441 c=$HOME/.paraslash/audiod.conf.min; s=server.foo.com
1442 formats="mp3 ogg aac wma" # remove what you do not have
1443 for f in $formats; do echo receiver \"$f:http -i $s\"; done > $c
1444 para_audiod --config $c
1445
1446 -------
1447 Filters
1448 -------
1449
1450 A paraslash filter is a module which transforms an input stream into
1451 an output stream. Filters are included in the para_audiod executable
1452 and in the stand-alone tool para_filter which usually contains the
1453 same modules.
1454
1455 While para_filter reads its input stream from STDIN and writes
1456 the output to STDOUT, the filter modules of para_audiod are always
1457 connected to a receiver which produces the input stream and a writer
1458 which absorbs the output stream.
1459
1460 Some filters depend on a specific library being installed and are
1461 not compiled in if this library was not found at compile time. To
1462 see the list of supported filters, run para_filter and para_audiod
1463 with the --help option. The output looks similar to the following:
1464
1465 Available filters:
1466 compress wav amp fecdec wmadec prebuffer oggdec aacdec mp3dec
1467
1468 Out of these filter modules, a chain of filters can be constructed,
1469 much in the way Unix pipes can be chained, and analogous to the use
1470 of modules in gstreamer: The output of the first filter becomes the
1471 input of the second filter. There is no limitation on the number of
1472 filters and the same filter may occur more than once.
1473
1474 Like receivers, each filter has its own command line options which
1475 must be quoted to protect them from the command line options of
1476 the driving application (para_audiod or para_filter). Example:
1477
1478 para_filter -f 'mp3dec --ignore-crc' -f 'compress --damp 1'
1479
1480 For para_audiod, each audio format has its own set of filters. The
1481 name of the audio format for which the filter should be applied is
1482 used as the prefix for the filter option. Example:
1483
1484 para_audiod -f 'mp3:prebuffer --duration 300'
1485
1486 Decoders
1487 ~~~~~~~~
1488
1489 For each supported audio format there is a corresponding filter
1490 which decodes audio data in this format to 16 bit PCM data which
1491 can be directly sent to the sound device or any other software that
1492 operates on undecoded PCM data (visualizers, equalizers etc.). Such
1493 filters are called _decoders_ in general, and xxxdec is the name of
1494 the paraslash decoder for the audio format xxx. For example, the mp3
1495 decoder filter is called mp3dec.
1496
1497 Note that the output of the decoder is about 10 times larger than
1498 its input. This means that filters that operate on the decoded audio
1499 stream have to deal with much more data than filters that transform
1500 the audio stream before it is fed to the decoder.
1501
1502 Paraslash relies on external libraries for most decoders, so these
1503 libraries must be installed for the decoder to be included in the
1504 para_filter and para_audiod executables. The oggdec filter depends
1505 on the libogg and libvorbis libraries for example.
1506
1507 Forward error correction
1508 ~~~~~~~~~~~~~~~~~~~~~~~~
1509
1510 As already mentioned REFERENCE(Streaming protocols, earlier),
1511 paraslash uses forward error correction (FEC) for the unreliable UDP
1512 and DCCP transports. FEC is a technique which was invented already
1513 in 1960 by Reed and Solomon and which is widely used for the parity
1514 calculations of storage devices (RAID arrays). It is based on the
1515 algebraic concept of finite fields, today called Galois fields, in
1516 honour of the mathematician Galois (1811-1832). The FEC implementation
1517 of paraslash is based on code by Luigi Rizzo.
1518
1519 Although the details require a sound knowledge of the underlying
1520 mathematics, the basic idea is not hard to understand: For positive
1521 integers k and n with k < n it is possible to compute for any k given
1522 data bytes d_1, ..., d_k the corresponding r := n -k parity bytes p_1,
1523 ..., p_r such that all data bytes can be reconstructed from *any*
1524 k bytes of the set
1525
1526 {d_1, ..., d_k, p_1, ..., p_r}.
1527
1528 FEC-encoding for unreliable network transports boils down to slicing
1529 the audio stream into groups of k suitably sized pieces called _slices_
1530 and computing the r corresponding parity slices. This step is performed
1531 in para_server which then sends both the data and the parity slices
1532 over the unreliable network connection. If the client was able
1533 to receive at least k of the n = k + r slices, it can reconstruct
1534 (FEC-decode) the original audio stream.
1535
1536 From these observations it is clear that there are three different
1537 FEC parameters: The slice size, the number of data slices k, and the
1538 total number of slices n. It is crucial to choose the slice size
1539 such that no fragmentation of network packets takes place because
1540 FEC only guards against losses and reodering but fails if slices are
1541 received partially.
1542
1543 FEC decoding in paralash is performed through the fecdec filter which
1544 usually is the first filter (there can be other filters before fecdec
1545 if these do not alter the audio stream).
1546
1547
1548 Volume adjustment (amp and compress)
1549 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1550
1551 The amp and the compress filter both adjust the volume of the audio
1552 stream. These filters operate on uncompressed audio samples. Hence
1553 they are usually placed directly after the decoding filter. Each
1554 sample is multiplied with a scaling factor (>= 1) which makes amp
1555 and compress quite expensive in terms of computing power.
1556
1557 *amp*
1558
1559 The amp filter amplifies the audio stream by a fixed scaling factor
1560 that must be known in advance. For para_audiod this factor is derived
1561 from the amplification field of the audio file's entry in the audio
1562 file table while para_filter uses the value given at the command line.
1563
1564 The optimal scaling factor F for an audio file is the largest real
1565 number F >= 1 such that after multiplication with F all samples still
1566 fit into the sample interval [-32768, 32767]. One can use para_filter
1567 in combination with the sox utility to compute F:
1568
1569 para_filter -f mp3dec -f wav < file.mp3 | sox -t wav - -e stat -v
1570
1571 The amplification value V which is stored in the audio file table,
1572 however, is an integer between 0 and 255 which is connected to F
1573 through the formula
1574
1575 V = (F - 1) * 64.
1576
1577 To store V in the audio file table, the command
1578
1579 para_client -- touch -a=V file.mp3
1580
1581 is used. The reader is encouraged to write a script that performs
1582 these computations :)
1583
1584 *compress*
1585
1586 Unlike the amplification filter, the compress filter adjusts the volume
1587 of the audio stream dynamically without prior knowledge about the peak
1588 value. It maintains the maximal volume of the last n samples of the
1589 audio stream and computes a suitable amplification factor based on that
1590 value and the various configuration options. It tries to chose this
1591 factor such that the adjusted volume meets the desired target level.
1592
1593 Note that it makes sense to combine amp and compress.
1594
1595 Misc filters (wav and prebuffer)
1596 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1597
1598 These filters are rather simple and do not modify the audio stream at
1599 all. The wav filter is only useful with para_filter and in connection
1600 with a decoder. It asks the decoder for the number of channels and the
1601 sample rate of the stream and adds a Microsoft wave header containing
1602 this information at the beginning. This allows to write wav files
1603 rather than raw PCM files (which do not contain any information about
1604 the number of channels and the sample rate).
1605
1606 The prebuffer filter simply delays the output until the given time has
1607 passed (starting from the time the first byte was available in its
1608 input queue) or until the given amount of data has accumulated. It
1609 is mainly useful for para_audiod if the standard parameters result
1610 in buffer underruns.
1611
1612 Both filters require almost no additional computing time, even when
1613 operating on uncompressed audio streams, since data buffers are simply
1614 "pushed down" rather than copied.
1615
1616 Examples
1617 ~~~~~~~~
1618
1619 -> Decode an mp3 file to wav format:
1620
1621 para_filter -f mp3dec -f wav < file.mp3 > file.wav
1622
1623 -> Amplify a raw audio file by a factor of 1.5:
1624
1625 para_filter -f amp --amp 32 < foo.raw > bar.raw
1626
1627 ------
1628 Output
1629 ------
1630
1631 Once an audio stream has been received and decoded to PCM format,
1632 it can be sent to a sound device for playback. This part is performed
1633 by paraslash _writers_ which are described in this chapter.
1634
1635 Writers
1636 ~~~~~~~
1637
1638 A paraslash writer acts as a data sink that consumes but does not
1639 produce audio data. Paraslash writers operate on the client side and
1640 are contained in para_audiod and in the stand-alone tool para_write.
1641
1642 The para_write program reads uncompressed audio data from STDIN. If
1643 this data starts with a wav header, sample rate, sample format and
1644 channel count are read from the header. Otherwise CD audio (44.1KHz
1645 16 bit little endian, stereo) is assumed but this can be overridden
1646 by command line options. para_audiod, on the other hand, obtains
1647 the sample rate and the number of channels from the decoder.
1648
1649 Like receivers and filters, each writer has an individual set of
1650 command line options, and for para_audiod writers can be configured
1651 per audio format separately. It is possible to activate more than
1652 one writer for the same stream simultaneously.
1653
1654 OS-dependent APIs
1655 ~~~~~~~~~~~~~~~~~
1656
1657 Unfortunately, the various flavours of Unix on which paraslash
1658 runs on have different APIs for opening a sound device and starting
1659 playback. Hence for each such API there is a paraslash writer that
1660 can play the audio stream via this API.
1661
1662 *ALSA*. The _Advanced Linux Sound Architecture_ is only available on
1663 Linux systems. Although there are several mid-layer APIs in use by
1664 the various Linux distributions (ESD, Jack, PulseAudio), paraslash
1665 currently supports only the low-level ALSA API which is not supposed
1666 to be change. ALSA is very feature-rich, in particular it supports
1667 software mixing via its DMIX plugin. ALSA is the default writer on
1668 Linux systems.
1669
1670 *OSS*. The _Open Sound System_ is the only API on *BSD Unixes and
1671 is also available on Linux systems, usually provided by ALSA as an
1672 emulation for backwards compatibility. This API is rather simple but
1673 also limited. For example only one application can open the device
1674 at any time. The OSS writer is activated by default on BSD Systems.
1675
1676 *OSX*. Mac OS X has yet another API called CoreAudio. The OSX writer
1677 for this API is only compiled in on such systems and is of course
1678 the default there.
1679
1680 *FILE*. The file writer allows to capture the audio stream and
1681 write the PCM data to a file on the file system rather than playing
1682 it through a sound device. It is supported on all platforms and is
1683 always compiled in.
1684
1685 *AO*. _Libao_ is a cross-platform audio library which supports a wide
1686 variety of platforms including PulseAudio (gnome), ESD (Enlightened
1687 Sound Daemon), AIX, Solaris and IRIX. The ao writer plays audio
1688 through an output plugin of libao.
1689
1690 Examples
1691 ~~~~~~~~
1692
1693 -> Use the OSS writer to play a wav file:
1694
1695 para_write --writer oss < file.wav
1696
1697 -> Enable ALSA software mixing for mp3 streams
1698
1699 para_audiod --writer 'mp3:alsa -d plug:swmix'
1700
1701
1702 ---
1703 Gui
1704 ---
1705
1706 para_gui executes an arbitrary command which is supposed to print
1707 status information to STDOUT. It then displays this information in
1708 a curses window. By default the command
1709
1710 para_audioc -- stat -p
1711
1712 is executed, but this can be customized via the --stat_cmd option. In
1713 particular it possible to use
1714
1715 para_client -- stat -p
1716
1717 to make para_gui work on systems on which para_audiod is not running.
1718
1719 Key bindings
1720 ~~~~~~~~~~~~
1721
1722 It is possible to bind keys to arbitrary commands via custom
1723 key-bindings. Besides the internal keys which can not be changed (help,
1724 quit, loglevel, version...), the following flavours of key-bindings
1725 are supported:
1726
1727 - external: Shutdown curses before launching the given command.
1728 Useful for starting other ncurses programs from within
1729 para_gui, e.g. aumix or dialog scripts. Or, use the mbox
1730 output format to write a mailbox containing one mail for each
1731 (admissible) file the audio file selector knows about. Then
1732 start mutt from within para_gui to browse your collection!
1733
1734 - display: Launch the command and display its stdout in
1735 para_gui's bottom window.
1736
1737 - para: Like display, but start "para_client <specified
1738 command>" instead of "<specified command>".
1739
1740 The general form of a key binding is
1741
1742 key_map k:m:c
1743
1744 which maps key k to command c using mode m. Mode may be x, d or p
1745 for external, display and paraslash commands, respectively.
1746
1747 Themes
1748 ~~~~~~
1749
1750 Currently there are only two themes for para_gui. It is easy, however,
1751 to add more themes. To create a new theme one has to define the
1752 position, color and geometry for for each status item that should be
1753 shown by this theme. See gui_theme.c for examples.
1754
1755 The "." and "," keys are used to switch between themes.
1756
1757 Examples
1758 ~~~~~~~~
1759
1760 -> Show server info:
1761
1762 key_map "i:p:si"
1763
1764 -> Jump to the middle of the current audio file by pressing F5:
1765
1766 key_map "<F5>:p:jmp 50"
1767
1768 -> vi-like bindings for jumping around:
1769
1770 key_map "l:p:ff 10"
1771 key_map "h:p:ff 10-"
1772 key_map "w:p:ff 60"
1773 key_map "b:p:ff 60-"
1774
1775 -> Print the current date and time:
1776
1777 key_map "D:d:date"
1778
1779 -> Call other curses programs:
1780
1781 key_map "U:x:aumix"
1782 key_map "!:x:/bin/bash"
1783 key_map "^E:x:/bin/sh -c 'vi ~/.paraslash/gui.conf'"
1784
1785 -----------
1786 Development
1787 -----------
1788
1789 Tools
1790 ~~~~~
1791
1792 In order to compile the sources from the git repository (rather than
1793 from tar balls) and for contributing non-trivial changes to the
1794 paraslash project, some additional tools should be installed on a
1795 developer machine.
1796
1797 http://git.or.cz/ (git). As described in more detail REFERENCE(Git
1798 branches, below), the git source code management tool is used for
1799 paraslash development. It is necessary for cloning the git repository
1800 and for getting updates.
1801
1802 ftp://ftp.gnu.org/pub/gnu/gengetopt/ (gengetopt). The C code for
1803 the command line parsers of all paraslash executables is generated
1804 by gengetopt. The generated C files are shipped in the tarballs but
1805 are not contained in the git repository.
1806
1807 ftp://ftp.gnu.org/pub/gnu/m4/ (m4). Some input files for gengetopt
1808 are generated from templates by the m4 macro processor.
1809
1810 ftp://ftp.gnu.org/pub/gnu/autoconf/ (autoconf) GNU autoconf creates
1811 the configure file which is shipped in the tarballs but has to be
1812 generated when compiling from git.
1813
1814 http://www.triptico.com/software/grutatxt.html (grutatxt). The
1815 HTML version of this manual and some of the paraslash web pages are
1816 generated by the grutatxt plain text to HTML converter. If changes
1817 are made to these text files the grutatxt package must be installed
1818 to regenerate the HTML files.
1819
1820 http://www.stack.nl/~dimitri/doxygen/ (doxygen). The documentation
1821 of paraslash's C sources uses the doxygen documentation system. The
1822 conventions for documenting the source code is described in the
1823 REFERENCE(Doxygen, Doxygen section).
1824
1825 ftp://ftp.gnu.org/pub/gnu/global (global). This is used to generate
1826 browsable HTML from the C sources. It is needed by doxygen.
1827
1828 Git branches
1829 ~~~~~~~~~~~~
1830
1831 Paraslash has been developed using the git source code management
1832 tool since 2006. Development is organized roughly in the same spirit
1833 as the git development itself, as described below.
1834
1835 The following text passage is based on "A note from the maintainer",
1836 written by Junio C Hamano, the maintainer of git.
1837
1838 There are four branches in the paraslash repository that track the
1839 source tree: "master", "maint", "next", and "pu".
1840
1841 The "master" branch is meant to contain what is well tested and
1842 ready to be used in a production setting. There could occasionally be
1843 minor breakages or brown paper bag bugs but they are not expected to
1844 be anything major, and more importantly quickly and easily fixable.
1845 Every now and then, a "feature release" is cut from the tip of this
1846 branch, named with three dotted decimal digits, like 0.4.2.
1847
1848 Whenever changes are about to be included that will eventually lead to
1849 a new major release (e.g. 0.5.0), a "maint" branch is forked off from
1850 "master" at that point. Obvious, safe and urgent fixes after the major
1851 release are applied to this branch and maintenance releases are cut
1852 from it. New features never go to this branch. This branch is also
1853 merged into "master" to propagate the fixes forward.
1854
1855 A trivial and safe enhancement goes directly on top of "master".
1856 New development does not usually happen on "master", however.
1857 Instead, a separate topic branch is forked from the tip of "master",
1858 and it first is tested in isolation; Usually there are a handful such
1859 topic branches that are running ahead of "master". The tip of these
1860 branches is not published in the public repository to keep the number
1861 of branches that downstream developers need to worry about low.
1862
1863 The quality of topic branches varies widely. Some of them start out as
1864 "good idea but obviously is broken in some areas" and then with some
1865 more work become "more or less done and can now be tested by wider
1866 audience". Luckily, most of them start out in the latter, better shape.
1867
1868 The "next" branch is to merge and test topic branches in the latter
1869 category. In general, this branch always contains the tip of "master".
1870 It might not be quite rock-solid production ready, but is expected to
1871 work more or less without major breakage. The maintainer usually uses
1872 the "next" version of paraslash for his own pleasure, so it cannot
1873 be _that_ broken. The "next" branch is where new and exciting things
1874 take place.
1875
1876 The two branches "master" and "maint" are never rewound, and "next"
1877 usually will not be either (this automatically means the topics that
1878 have been merged into "next" are usually not rebased, and you can find
1879 the tip of topic branches you are interested in from the output of
1880 "git log next"). You should be able to safely build on top of them.
1881
1882 However, at times "next" will be rebuilt from the tip of "master" to
1883 get rid of merge commits that will never be in "master. The commit
1884 that replaces "next" will usually have the identical tree, but it
1885 will have different ancestry from the tip of "master".
1886
1887 The "pu" (proposed updates) branch bundles the remainder of the
1888 topic branches. The "pu" branch, and topic branches that are only in
1889 "pu", are subject to rebasing in general. By the above definition
1890 of how "next" works, you can tell that this branch will contain quite
1891 experimental and obviously broken stuff.
1892
1893 When a topic that was in "pu" proves to be in testable shape, it
1894 graduates to "next". This is done with
1895
1896 git checkout next
1897 git merge that-topic-branch
1898
1899 Sometimes, an idea that looked promising turns out to be not so good
1900 and the topic can be dropped from "pu" in such a case.
1901
1902 A topic that is in "next" is expected to be polished to perfection
1903 before it is merged to "master". Similar to the above, this is
1904 done with
1905
1906 git checkout master
1907 git merge that-topic-branch
1908 git branch -d that-topic-branch
1909
1910 Note that being in "next" is not a guarantee to appear in the next
1911 release (being in "master" is such a guarantee, unless it is later
1912 found seriously broken and reverted), nor even in any future release.
1913
1914 Coding Style
1915 ~~~~~~~~~~~~
1916
1917 The preferred coding style for paraslash coincides more or less
1918 with the style of the Linux kernel. So rather than repeating what is
1919 written XREFERENCE(http://www.kernel.org/doc/Documentation/CodingStyle,
1920 there), here are the most important points.
1921
1922 - Burn the GNU coding standards.
1923 - Never use spaces for indentation.
1924 - Tabs are 8 characters, and thus indentations are also 8 characters.
1925 - Don't put multiple assignments on a single line.
1926 - Avoid tricky expressions.
1927 - Don't leave whitespace at the end of lines.
1928 - The limit on the length of lines is 80 columns.
1929 - Use K&R style for placing braces and spaces:
1930
1931 if (x is true) {
1932 we do y
1933 }
1934
1935 - Use a space after (most) keywords.
1936 - Do not add spaces around (inside) parenthesized expressions.
1937 - Use one space around (on each side of) most binary and ternary operators.
1938 - Do not use cute names like ThisVariableIsATemporaryCounter, call it tmp.
1939 - Mixed-case names are frowned upon.
1940 - Descriptive names for global variables are a must.
1941 - Avoid typedefs.
1942 - Functions should be short and sweet, and do just one thing.
1943 - The number of local variables shouldn't exceed 10.
1944 - Gotos are fine if they improve readability and reduce nesting.
1945 - Don't use C99-style "// ..." comments.
1946 - Names of macros defining constants and labels in enums are capitalized.
1947 - Enums are preferred when defining several related constants.
1948 - Always use the paraslash wrappers for allocating memory.
1949 - If the name of a function is an action or an imperative.
1950 command, the function should return an error-code integer
1951 (<0 means error, >=0 means success). If the name is a
1952 predicate, the function should return a "succeeded" boolean.
1953
1954
1955 Doxygen
1956 ~~~~~~~
1957
1958 Doxygen is a documentation system for various programming
1959 languages. The paraslash project uses Doxygen for generating the API
1960 reference on the web pages, but good source code documentation is
1961 also beneficial to people trying to understand the code structure
1962 and the interactions between the various source files.
1963
1964 It is more illustrative to look at the source code for examples than
1965 to describe the conventions for documenting the source in this manual,
1966 so we only describe which parts of the code need doxygen comments,
1967 but leave out details on documentation conventions.
1968
1969 As a rule, only the public part of the C source is documented with
1970 Doxygen. This includes structures, defines and enumerations in header
1971 files as well as public (non-static) C functions. These should be
1972 documented completely. For example each parameter and the return
1973 value of a public function should get a descriptive comment.
1974
1975 No doxygen comments are necessary for static functions and for
1976 structures and enumerations in C files (which are used only within
1977 this file). This does not mean, however, that those entities need
1978 no documentation at all. Instead, common sense should be applied to
1979 document what is not obvious from reading the code.
1980
1981 --------
1982 Appendix
1983 --------
1984
1985 Network protocols
1986 ~~~~~~~~~~~~~~~~~
1987
1988 *IP*. The _Internet Protocol_ is the primary networking protocol
1989 used for the Internet. All protocols described below use IP as the
1990 underlying layer. Both the prevalent IPv4 and the next-generation
1991 IPv6 variant are being deployed actively worldwide.
1992
1993 *Connection-oriented and connectionless protocols*. Connectionless
1994 protocols differ from connection-oriented ones in that state
1995 associated with the sending/receiving endpoints is treated
1996 implicitly. Connectionless protocols maintain no internal knowledge
1997 about the state of the connection. Hence they are not capable of
1998 reacting to state changes, such as sudden loss or congestion on the
1999 connection medium. Connection-oriented protocols, in contrast, make
2000 this knowledge explicit. The connection is established only after
2001 a bidirectional handshake which requires both endpoints to agree
2002 on the state of the connection, and may also involve negotiating
2003 specific parameters for the particular connection. Maintaining an
2004 up-to-date internal state of the connection also in general means
2005 that the sending endpoints perform congestion control, adapting to
2006 qualitative changes of the connection medium.
2007
2008 *Reliability*. In IP networking, packets can be lost, duplicated,
2009 or delivered out of order, and different network protocols handle
2010 these problems in different ways. We call a transport-layer protocol
2011 _reliable_, if it turns the unreliable IP delivery into an ordered,
2012 duplicate- and loss-free delivery of packets. Sequence numbers
2013 are used to discard duplicates and re-arrange packets delivered
2014 out-of-order. Retransmission is used to guarantee loss-free
2015 delivery. Unreliable protocols, in contrast, do not guarantee ordering
2016 or data integrity.
2017
2018 *Classification*. With these definitions the protocols which are used
2019 by paraslash for steaming audio data may be classified as follows.
2020
2021 - HTTP/TCP: connection-oriented, reliable,
2022 - UDP: connectionless, unreliable,
2023 - DCCP: connection-oriented, unreliable.
2024
2025 Below we give a short descriptions of these protocols.
2026
2027 *TCP*. The _Transmission Control Protocol_ provides reliable,
2028 ordered delivery of a stream and a classic window-based congestion
2029 control. In contrast to UDP and DCCP (see below), TCP does not have
2030 record-oriented or datagram-based syntax, i.e. it provides a stream
2031 which is unaware and independent of any record (packet) boundaries.
2032 TCP is used extensively by many application layers. Besides HTTP (the
2033 Hypertext Transfer Protocol), also FTP (the File Transfer protocol),
2034 SMTP (Simple Mail Transfer Protocol), SSH (Secure Shell) all sit on
2035 top of TCP.
2036
2037 *UDP*. The _User Datagram Protocol_ is the simplest transport-layer
2038 protocol, built as a thin layer directly on top of IP. For this reason,
2039 it offers the same best-effort service as IP itself, i.e. there is no
2040 detection of duplicate or reordered packets. Being a connectionless
2041 protocol, only minimal internal state about the connection is
2042 maintained, which means that there is no protection against packet
2043 loss or network congestion. Error checking and correction (if at all)
2044 are performed in the application.'
2045
2046 *DCCP*. The _Datagram Congestion Control Protocol_ combines the
2047 connection-oriented state maintenance known from TCP with the
2048 unreliable, datagram-based transport of UDP. This means that it
2049 is capable of reacting to changes in the connection by performing
2050 congestion control, offering multiple alternative approaches. But it
2051 is bound to datagram boundaries (the maximum packet size supported
2052 by a medium), and like UDP it lacks retransmission to protect
2053 against loss. Due to the use of sequence numbers, it is however
2054 able to react to loss (interpreted as a congestion indication) and
2055 to ignore out-of-order and duplicate packets. Unlike TCP it allows
2056 to negotiate specific, binding features for a connection, such as
2057 the choice of congestion control: classic, window-based congestion
2058 control known from TCP is available as CCID-2, rate-based, "smooth"
2059 congestion control is offered as CCID-3.
2060
2061 *HTTP*. _The Hypertext Transfer Protocol_ is an application layer
2062 protocol on top of TCP. It is spoken by web servers and is most often
2063 used for web services. However, as can be seen by the many Internet
2064 radio stations and YouTube/Flash videos, http is by far not limited to
2065 the delivery of web pages only. Being a simple request/response based
2066 protocol, the semantics of the protocol also allow the delivery of
2067 multimedia content, such as audio over http.
2068
2069 *Multicast*. IP multicast is not really a protocol but a technique
2070 for one-to-many communication over an IP network. The challenge is to
2071 deliver information to a group of destinations simultaneously using
2072 the most efficient strategy to send the messages over each link of
2073 the network only once. This has benefits for streaming multimedia:
2074 the standard one-to-one unicast offered by TCP/DCCP means that
2075 n clients listening to the same stream also consume n-times the
2076 resources, whereas multicast requires to send the stream just once,
2077 irrespective of the number of receivers. Since it would be costly to
2078 maintain state for each listening receiver, multicast often implies
2079 connectionless transport, which is the reason that it is currently
2080 only available via UDP.
2081
2082 License
2083 ~~~~~~~
2084
2085 Paraslash is licensed under the GPL, version 2. Most of the code
2086 base has been written from scratch, and those parts are GPL V2
2087 throughout. Notable exceptions are FEC and the WMA decoder. See the
2088 corresponding source files for licencing details for these parts. Some
2089 code sniplets of several other third party software packages have
2090 been incorporated into the paraslash sources, for example log message
2091 coloring was taken from the git sources. These third party software
2092 packages are all published under the GPL or some other license
2093 compatible to the GPL.
2094
2095 Acknowledgements
2096 ~~~~~~~~~~~~~~~~
2097
2098 Many thanks to Gerrit Renker who read an early draft of this manual
2099 and contributed significant improvements.
2100
2101 ----------
2102 References
2103 ----------
2104
2105 Articles
2106 ~~~~~~~~
2107 - Reed, Irving S.; Solomon, Gustave (1960),
2108 XREFERENCE(http://kom.aau.dk/~heb/kurser/NOTER/KOFA01.PDF,
2109 Polynomial Codes over Certain Finite Fields), Journal of the
2110 Society for Industrial and Applied Mathematics (SIAM) 8 (2):
2111 300-304, doi:10.1137/0108018)
2112
2113 RFCs
2114 ~~~~
2115
2116 - XREFERENCE(http://www.ietf.org/rfc/rfc768.txt, RFC 768) (1980):
2117 User Datagram Protocol
2118 - XREFERENCE(http://www.ietf.org/rfc/rfc791.txt, RFC 791) (1981):
2119 Internet Protocol
2120 - XREFERENCE(http://www.ietf.org/rfc/rfc2437.txt, RFC 2437) (1998):
2121 RSA Cryptography Specifications
2122 - XREFERENCE(http://www.ietf.org/rfc/rfc4340.txt, RFC 4340)
2123 (2006): Datagram Congestion Control Protocol (DCCP)
2124 - XREFERENCE(http://www.ietf.org/rfc/rfc4341.txt, RFC 4341) (2006):
2125 Congestion Control ID 2: TCP-like Congestion Control
2126 - XREFERENCE(http://www.ietf.org/rfc/rfc4342.txt, RFC 4342) (2006):
2127 Congestion Control ID 3: TCP-Friendly Rate Control (TFRC)
2128
2129 Application web pages
2130 ~~~~~~~~~~~~~~~~~~~~~
2131
2132 - XREFERENCE(http://paraslash.systemlinux.org/, paraslash)
2133 - XREFERENCE(http://xmms2.org/wiki/Main_Page, xmms)
2134 - XREFERENCE(http://www.mpg123.de/, mpg123)
2135 - XREFERENCE(http://gstreamer.freedesktop.org/, gstreamer)
2136 - XREFERENCE(http://www.icecast.org/, icecast)
2137 - XREFERENCE(http://beesbuzz.biz/code/audiocompress.php, Audio Compress)
2138
2139 External documentation
2140 ~~~~~~~~~~~~~~~~~~~~~~
2141
2142 - XREFERENCE(http://kernel.org/pub/linux/kernel/people/hpa/raid6.pdf,
2143 H. Peter Anvin: The mathematics of Raid6)
2144 - XREFERENCE(http://info.iet.unipi.it/~luigi/fec_ccr.ps.gz,
2145 Luigi Rizzo: Effective Erasure Codes for reliable Computer
2146 Communication Protocols)
2147
2148 Code
2149 ~~~~
2150 - XREFERENCE(http://info.iet.unipi.it/~luigi/vdm.tar.gz,
2151 Original FEC implementation by Luigi Rizzo)
2152