X-Git-Url: http://git.tuebingen.mpg.de/?p=paraslash.git;a=blobdiff_plain;f=web%2Fmanual.md;h=96d724c939ee13f1dd640ee98a47f1421bc1d85f;hp=ff99fb2046f2fc5d5607a6daba8ba50f794cda4b;hb=6811b2f8ea8b7a8c77046285c9432aee6327da80;hpb=c5f8faf9c0f0a63422982f87073a68613b5d117e diff --git a/web/manual.md b/web/manual.md index ff99fb20..96d724c9 100644 --- a/web/manual.md +++ b/web/manual.md @@ -12,81 +12,143 @@ paraslash executable. Introduction ============ -In this chapter we give an [overview](#Overview) of the interactions of -the two main programs contained in the paraslash package, followed by +In this chapter we give an [overview](#Overview) of the interactions +of the programs contained in the paraslash package, followed by [brief descriptions](#The.paraslash.executables) of all executables. Overview -------- The core functionality of the para suite is provided by two main -executables, para_server and para_audiod. The former maintains a -database of audio files and streams these files to para_audiod which -receives and plays the stream. - -In a typical setting, both para_server and para_audiod act as -background daemons whose functionality is controlled by client -programs: the para_audioc client controls para_audiod over a local -socket while the para_client program connects to para_server over a -local or remote networking connection. - -Typically, these two daemons run on different hosts but a local setup -is also possible. +applications, para_server and para_audiod. para_server maintains +the audio file database and acts as the streaming source, while +para_audiod is the streaming client. Usually, both run in the +background on different hosts but a local setup is also possible. A simplified picture of a typical setup is as follows - server_host client_host - ~~~~~~~~~~~ ~~~~~~~~~~~ - +-----------+ audio stream +-----------+ - |para_server| -----------------------------> |para_audiod| - +-----------+ +-----------+ - ^ ^ - | | - | | connect - | | - | | - | +-----------+ - | |para_audioc| - | +-----------+ - | - | - | connect +-----------+ - +-------------------------------------- |para_client| - +-----------+ + .____________________. + | ______ | + .-----------------------. | .d########b. | + |.---------------------.| | .d############b | + || || | .d######""####//b. | + || || | 9######( )######P | + || || | 'b######++######d' | + || Screen || | "9############P" | + || || | "9a########P" | + || || | `""""'' | + |`---------------------'| | ________________ | + `-----------------------' | |________________| | + ___) (___ |____________________| + `-._______.-' loudspeaker + | | + | | + | | + .____/ \___. ._____________. ._____/ \_____. + | | | | | | + | para_gui |-----| para_audioc |-----| para_audiod | + |____ ___| |_____________| |_____ _____| + \ / \ / + | | + | | + | | + ._____/ \_____. ._____/ \_____. + | | | | + | para_client |-----------------------| para_server | + |_____________| |_____ _____| + \ / + | + | + .-'"""`-. + ( ) + |`-.___.-'| + | | + |. ' " ` .| + | | + `-.___.-' + Database + +The two client programs, para_client and para_audioc communicate with +para_server and para_audiod, respectively. + +para_gui controls para_server and para_audiod by executing para_client +and para_audioc. In particular, it runs a command to obtain the state +of para_audiod and para_server, and the metadata of the current audio +file. This information is pretty-printed in a curses window. + The paraslash executables ------------------------- -### para_server ### +

para_server

para_server streams binary audio data (MP3, ...) over local and/or remote networks. It listens on a TCP port and accepts commands such -as play, stop, pause, next from authenticated clients. There are -many more commands though, see the man page of para_server for a -description of all commands. - -It supports three built-in network streaming protocols -(senders/receivers): HTTP, DCCP, or UDP. This is explained in more -detail in the section on [networking](#Networking). - -The built-in audio file selector of paraslash is used to manage your -audio files. It maintains statistics on the usage of all available -audio files such as last-played time, and the number of times each -file was selected. - -Additional information may be added to the database to allow +as play, stop, pause, next from authenticated clients. The components +of para_server are illustrated in the following diagram: + + ______________________________________________________________________ network + | | | | | + | .-'""""`-. | | | | + | ( ) | | | | + .____/ \_____. |`-.____.-'| .____/ \____/ \____/ \____. | + | | | | | | | + | dispatcher | | database | | senders (http/udp/dccp) | | + |____ _____| | | |___________ ___________| | + \ / |. ' "" ` .| \ / | + | | | | | + | `-.____.-' | | + | | | | + | | | | + | | | | + | ._____/ \_____. .________/ \________. | + | | | | | | + | | audio file |________| virtual streaming | | + | | selector | | system | | + | |_____ _____| |________ ________| | + | \ / \ / | + | | | | + | | | | + | | ._________________. | | + | | | | | | + | `---| command handler |---' | + | |____ ___ ____| | + | \ / \ / | + | | | | + | | | | + | | | | + `-------------------------' `--------------------------' + + +Incoming connections arrive at the dispatcher which creates a process +dedicated to the connection. Its task is to authenticate the client +and to run the command handler which forwards the client request to +either the audio file selector or the virtual streaming system. Results +(if any) are sent back to the client. + +The audio file selector manages audio files using various database +tables. It maintains statistics on the usage of all audio files such as +last-played time and the number of times each file was selected. It +is also responsible for selecting and loading audio files for +streaming. Additional information may be added to the database to allow fine-grained selection based on various properties of the audio file, -including information found in (ID3) tags. However, old-fashioned -playlists are also supported. - -It is also possible to store images (album covers) and lyrics in the -database and associate these to the corresponding audio files. - +including information found in (ID3) tags. Simple playlists are also +supported. It is possible to store images (album covers) and lyrics +in the database and associate these to the corresponding audio files. The section on the [audio file selector](#The.audio.file.selector) -discusses this topic. +discusses this topic in more detail. +Another component of para_server is the virtual streaming system, +which controls the paraslash senders. During streaming it requests +small chunks of data (e.g., mp3 frames) from the audio file selector +and feeds them to the senders which forward the chunks to connected +clients. -### para_client ### +The three senders of para_server correspond to network streaming +protocols based on HTTP, DCCP, or UDP. This is explained in the +section on [networking](#Networking). + +

para_client

The client program to connect to para_server. paraslash commands are sent to para_server and the response is dumped to STDOUT. This @@ -101,29 +163,67 @@ If para_client is started without non-option arguments, an interactive session (shell) is started. Command history and command completion are supported through libreadline. -### para_audiod ### - -The local daemon that collects information from para_server. - -It runs on the client side and connects to para_server. As soon as -para_server announces the availability of an audio stream, para_audiod -starts an appropriate receiver, any number of filters and a paraslash -writer to play the stream. - -Moreover, para_audiod listens on a local socket and sends status -information about para_server and para_audiod to local clients on -request. Access via this local socket may be restricted by using Unix -socket credentials, if available. - - -### para_audioc ### +

para_audiod

+ +The purpose of para_audiod is to download, decode and play an audio +stream received from para_server. A typical setup looks as follows. + + + .----------------------------. + | | + | | + ._____/ \_____. .___/ \____. + | | .----------| | + | para_server | | .______| receiver | + |_____ ____| | | |___ ____| + \ / | | \ / + | | | | + | | | | + | | | | + ._____/ \_____. | | .___/ \____. + | | | | | | + | status task |-----+ | | filter 1 | + |_____________| | |___ ____| + | \ / + | | .____________________. + | | | ______ | + .____________. | .___/ \____. | .d########b. | + | | | | | | .d############b | + | dispatcher |----------' | filter 2 | | .d######""####//b. | + |_____ ____| |___ ____| | 9######( )######P | + \ / \ / | 'b######++######d' | + | | | "9############P" | + | | | "9a########P" | + ._____/ \_____. .___/ \____. | `""""'' | + | | | | | ________________ | + | para_audioc | | writer |------| |________________| | + |_____________| |__________| |____________________| + + +The status task of para_audiod connects to para_server and runs the +"stat" command to retrieve the current server status. If an audio +stream is available, para_audiod starts a so-called buffer tree to +play the stream. + +The buffer tree consists of a receiver, any number of filters and a +writer. The receiver downloads the audio stream from para_server and +the filters decode or modify the received data. The writer plays the +decoded stream. + +The dispatcher of para_audiod listens on a local socket and runs +audiod commands on behalf of para_audioc. For example, para_gui runs +para_audioc to obtain status information about para_audiod and the +current audio file. Access to the local socket may be restricted by +means of Unix socket credentials. + +

para_audioc

The client program which talks to para_audiod. Used to control para_audiod, to receive status info, or to grab the stream at any point of the decoding process. Like para_client, para_audioc supports interactive sessions on systems with libreadline. -### para_recv ### +

para_recv

A command line HTTP/DCCP/UDP stream grabber. The http mode is compatible with arbitrary HTTP streaming sources (e.g. icecast). @@ -134,7 +234,7 @@ optionally 'just in time'. This allows to cut an audio file without first decoding it, and it enables third-party software which is unaware of the particular audio format to send complete frames in real time. -### para_filter ### +

para_filter

A filter program that reads from STDIN and writes to STDOUT. Like para_recv, this is an atomic building block which can be used to @@ -143,31 +243,33 @@ different functionalities in one tool: decoders for multiple audio formats and a number of processing filters, among these a normalizer for audio volume. -### para_afh ### +

para_afh

A small stand-alone program that prints tech info about the given audio file to STDOUT. It can be instructed to print a "chunk table", an array of offsets within the audio file. -### para_write ### +

para_write

A modular audio stream writer. It supports a simple file writer -output plug-in and optional WAV/raw players for ALSA (Linux) and for -coreaudio (Mac OS). para_write can also be used as a stand-alone WAV -or raw audio player. +output plug-in and optional WAV/raw players for ALSA (Linux) and OSS. +para_write can also be used as a stand-alone WAV or raw audio player. -### para_play ### +

para_play

-A command line audio player. +A command line audio player which supports the same audio formats as +para_server. It differs from other players in that it has an insert +and a command mode, like the vi editor. Line editing is based on +libreadline, and tab completion and command history are supported. -### para_gui ### +

para_gui

Curses-based gui that presents status information obtained in a curses window. Appearance can be customized via themes. para_gui provides key-bindings for the most common server commands and new key-bindings can be added easily. -### para_fade ### +

para_mixer

An alarm clock and volume-fader for OSS and ALSA. @@ -183,25 +285,28 @@ source code and the steps that have to be performed in order to Requirements ------------ -### For the impatient ### +

For the impatient

+ git clone git://git.tuebingen.mpg.de/lopsub + cd lopsub && make && sudo make install git clone git://git.tuebingen.mpg.de/osl cd osl && make && sudo make install && sudo ldconfig - sudo apt-get install autoconf libssl-dev help2man gengetopt m4 \ + sudo apt-get install autoconf libssl-dev m4 \ libmad0-dev libid3tag0-dev libasound2-dev libvorbis-dev \ libfaad-dev libspeex-dev libFLAC-dev libsamplerate-dev realpath \ libasound2-dev libao-dev libreadline-dev libncurses-dev \ libopus-dev -### Detailed description ### +

Detailed description

In any case you will need -- [libosl](http://people.tuebingen.mpg.de/maan/osl/). The _object -storage layer_ library is used by para_server. To clone the source -code repository, execute +- [lopsub](http://people.tuebingen.mpg.de/maan/lopsub/). The long +option parser for subcommands generates the command line and config +file parsers for all paraslash executables. Clone the source code +repository with - git clone git://git.tuebingen.mpg.de/osl + git clone git://git.tuebingen.mpg.de/lopsub - [gcc](ftp://ftp.gnu.org/pub/gnu/gcc) or [clang](http://clang.llvm.org). All gcc versions >= 4.2 are currently @@ -214,18 +319,17 @@ disto. On BSD systems the gnu make executable is often called gmake. during compilation require the _Bourne again shell_. It is most likely already installed. -- [gengetopt](ftp://ftp.gnu.org/pub/gnu/gengetopt/) is needed to -generate the C code for the command line parsers of all paraslash -executables. - -- [help2man](ftp://ftp.gnu.org/pub/gnu/help2man) is used to create -the man pages. - - [m4](ftp://ftp.gnu.org/pub/gnu/m4/). Some source files are generated from templates by the m4 macro processor. Optional: +- [libosl](http://people.tuebingen.mpg.de/maan/osl/). The _object +storage layer_ library is used by para_server. To clone the source +code repository, execute + + git clone git://git.tuebingen.mpg.de/osl + - [openssl](http://www.openssl.org/) or [libgcrypt](ftp://ftp.gnupg.org/gcrypt/libgcrypt/). At least one of these two libraries is needed as the backend for cryptographic @@ -249,8 +353,11 @@ recognized. The mp3 tagger also needs this library for modifying you need libogg, libvorbis, libvorbisfile. The corresponding Debian packages are called `libogg-dev` and `libvorbis-dev`. -- [libfaad](http://www.audiocoding.com/). For aac files (m4a) you -need libfaad (`libfaad-dev`). +- [libfaad and mp4ff](http://www.audiocoding.com/). For aac files +(m4a) you need libfaad and libmp4ff (package: `libfaad-dev`). Note +that for some distributions, e.g. Ubuntu, mp4ff is not part of the +libfaad package. Install the faad library from sources (available +through the above link) to get the mp4ff library and header files. - [speex](http://www.speex.org/). In order to stream or decode speex files, libspeex (`libspeex-dev`) is required. @@ -309,7 +416,7 @@ to install executables under /usr/local/bin and the man pages under Configuration ------------- -### Create a paraslash user ### +

Create a paraslash user

In order to control para_server at runtime you must create a paraslash user. As authentication is based on the RSA crypto system you'll have @@ -353,7 +460,7 @@ Finally, tell para_client to connect to server_host: echo 'hostname server_host' > $conf -### Start para_server ### +

Start para_server

For this first try, we'll use the info loglevel to make the output of para_server more verbose. @@ -369,7 +476,7 @@ commands. Open a new shell as bar@client_host and try to retrieve the list of available commands and some server info. Don't proceed if this doesn't work. -### Create and populate the database ### +

Create and populate the database

An empty database is created with @@ -397,7 +504,7 @@ You may print the list of all known audio files with para_client ls -### Configure para_audiod ### +

Configure para_audiod

We will have to tell para_audiod that it should receive the audio stream from server_host via http: @@ -418,14 +525,6 @@ in which order. Troubleshooting --------------- -If you receive a socket related error on server or audiod startup, -make sure you have write permissions to the /var/paraslash directory: - - sudo chown $LOGNAME /var/paraslash - -Alternatively, use the --afs-socket (para_server) or --socket -(para_audiod) option to specify a different socket pathname. - To identify streaming problems try to receive, decode and play the stream manually using para_recv, para_filter and para_write as follows. For simplicity we assume that you're running Linux/ALSA and that only @@ -448,9 +547,9 @@ User management para_server uses a challenge-response mechanism to authenticate requests from incoming connections, similar to ssh's public key authentication method. Authenticated connections are encrypted using -a stream cipher, either RC4 or AES in integer counter mode. +the AES stream cipher in integer counter mode. -In this chapter we briefly describe RSA, RC4 and AES, and sketch the +In this chapter we briefly describe RSA and AES, and sketch the [authentication handshake](#Client-server.authentication) between para_client and para_server. User management is discussed in the section on [the user_list file](#The.user_list.file). @@ -458,33 +557,33 @@ These sections are all about communication between the client and the server. Connecting para_audiod is a different matter and is described in a [separate section](#Connecting.para_audiod). -RSA, RC4, AES -------------- +RSA and AES +----------- -RSA is an asymmetric block cipher which is used in many applications, -including ssh and gpg. An RSA key consists in fact of two keys, +A block cipher is a transformation which operates on fixed-length +blocks. For symmetric block ciphers the transformation is determined +by a single key for both encryption and decryption. For asymmetric +block ciphers, on the other hand, the key consists of two parts, called the public key and the private key. A message can be encrypted -with either key and only the counterpart of that key can decrypt -the message. While RSA can be used for both signing and encrypting -a message, paraslash uses RSA only for the latter purpose. The -RSA public key encryption and signatures algorithms are defined in -detail in RFC 2437. - -RC4 is a stream cipher, i.e. the input is XORed with a pseudo-random -key stream to produce the output. Decryption uses the same function -calls as encryption. While RC4 supports variable key lengths, -paraslash uses a fixed length of 256 bits, which is considered a -strong encryption by today's standards. Since the same key must never -be used twice, a different, randomly-generated key is used for every -new connection. +with either key and only the counterpart of that key can decrypt the +message. Asymmetric block ciphers can be used for both signing and +encrypting a message. + +RSA is an asymmetric block cipher which is used in many applications, +including ssh and gpg. The RSA public key encryption and signatures +algorithms are defined in detail in RFC 2437. Paraslash relies on +RSA for authentication. + +Stream ciphers XOR the input with a pseudo-random key stream to produce +the output. Decryption uses the same function calls as encryption. +Any block cipher can be turned into a stream cipher by generating the +pseudo-random key stream by encrypting successive values of a counter +(counter mode). AES, the advanced encryption standard, is a well-known symmetric block -cipher, i.e. a transformation operating on fixed-length blocks which -is determined by a single key for both encryption and decryption. Any -block cipher can be turned into a stream cipher by generating -a pseudo-random key stream by encrypting successive values of a -counter. The AES_CTR128 stream cipher used in paraslash is obtained -in this way from the AES block cipher with a 128 bit block size. +cipher. Paraslash employs AES in counter mode as described above to +encrypt communications. Since a stream cipher key must not be used +twice, a random key is generated for every new connection. Client-server authentication ---------------------------- @@ -524,8 +623,8 @@ point on the communication is encrypted using the stream cipher with the session key known to both peers. paraslash relies on the quality of the pseudo-random bytes provided -by the crypto library (openssl or libgcrypt), on the security of the -implementation of the RSA, RC4 and AES crypto routines and on the +by the crypto library (openssl or libgcrypt), on the security of +the implementation of the RSA and AES crypto routines and on the infeasibility to invert the SHA1 function. Neither para_server or para_client create RSA keys on their @@ -567,8 +666,7 @@ execute. The output of para_client help -contains in the third column the permissions needed to execute the -command. +contains the permissions needed to execute the command. It is possible to make para_server reread the user_list file by executing the paraslash "hup" command or by sending SIGHUP to the @@ -594,27 +692,21 @@ The audio file selector paraslash comes with a sophisticated audio file selector (AFS), whose main task is to determine which file to stream next, based on information on the audio files stored in a database. It communicates -also with para_client whenever an AFS command is executed, for example -to answer a database query. +also with para_client via the command handler whenever an AFS command +is executed, for example to answer a database query. -Besides the traditional playlists, AFS supports audio file selection +Besides the simple playlists, AFS supports audio file selection based on _moods_ which act as a filter that limits the set of all -known audio files to those which satisfy certain criteria. It also +known audio files to those which satisfy certain criteria. It also maintains tables containing images (e.g. album cover art) and lyrics that can be associated with one or more audio files. -AFS employs [libosl](http://people.tuebingen.mpg.de/maan/osl/), the -object storage layer library, as the backend library for storing -information on audio files, playlists, etc. This library offers -functionality similar to a relational database, but is much more -lightweight than a full database backend. - In this chapter we sketch the setup of the [AFS process](#The.AFS.process) during server startup and proceed with the description of the [layout](#Database.layout) of the various database tables. The section on [playlists and moods](#Playlists.and.moods) explains these two audio file selection mechanisms in detail -and contains pratical examples. The way [file renames and content +and contains practical examples. The way [file renames and content changes](#File.renames.and.content.changes) are detected is discussed briefly before the [Troubleshooting](#Troubleshooting) section concludes the chapter. @@ -623,25 +715,85 @@ The AFS process --------------- On startup, para_server forks to create the AFS process which opens -the OSL database tables. The server process communicates with the -AFS process via pipes and shared memory. Usually, the AFS process -awakes only briefly whenever the current audio file changes. The AFS -process determines the next audio file, opens it, verifies it has -not been changed since it was added to the database and passes the -open file descriptor to the server process, along with audio file -meta-data such as file name, duration, audio format and so on. The -server process then starts to stream the audio file. - -The AFS process also accepts connections from local clients via -a well-known socket. However, only child processes of para_server -may connect through this socket. All server commands that have the -AFS_READ or AFS_WRITE permission bits use this mechanism to query or -change the database. +the database tables. The AFS process accepts incoming connections +which arrive either on a pipe which is shared with para_server, +or on the local socket it is listening on. The setup is as follows. + + .___________________. .______________. + | | | | + | virtual streaming | | audio format | + | system | | handler | + |_________ _______| |_____ ______| + \ / \ / + | | + .-'""""`-. | | .-'""""`-. + ( ) | | ( ) + |`-.____.-'| .__/ \________________/ \___. |`-.____.-'| + | | | | | | + | file |----| AFS (audio file selector) |----| OSL | + | system | | process | | database | + | | |___________________________| | | + |. ' "" ` .| | |. ' "" ` .| + | | | | | + `-.____.-' | `-.____.-' + ._______/ \_______. + | | + | command handler | + |_______ _______| + \ / + | + | + | + ._____/ \_____. + | | + | para_client | + |_____________| + +The virtual streaming system, which is part of the server process, +communicates with the AFS process via pipes and shared memory. When +the current audio file changes, it sends a notification through the +shared pipe. The AFS process queries the database to determine the +next audio file, opens it, verifies that it has not been changed since +it was added to the database and passes the open file descriptor back +to the virtual streaming system, along with audio file meta-data such +as file name, duration, audio format and so on. The virtual streaming +system then starts to stream the file. + +The command handlers of all AFS server commands use the local socket +to query or update the database. For example, the command handler of +the add command sends the path of an audio file to the local socket. +The AFS process opens the file and tries to find an audio format +handler which recognizes the file. If all goes well, a new database +entry with metadata obtained from the audio format handler is added +to the database. + +Note that AFS employs +[libosl](http://people.tuebingen.mpg.de/maan/osl/), the object +storage layer library, as the database backend. This library offers +functionality similar to a relational database, but is much more +lightweight than a full featured database management system. Database layout --------------- -### The audio file table ### +Metadata about the known audio files is stored in an OSL database. This +database consists of the following tables: + +- The audio file table contains path, hash and metadata of each +known file. + +- The "attributes" table maps each of the 64 possible attributes to a +string. + +- The "blob" tables store images, lyrics, moods, playlists. All of +these are optional. + +- The "score" table describes the subset of admissible files for the +current playlist or mood. + +All tables are described in more detail below. + +

The audio file table

This is the most important and usually also the largest table of the AFS database. It contains the information needed to stream each audio @@ -690,7 +842,7 @@ directory. In the latter case, the directory is traversed recursively and all files which are recognized as valid audio files are added to the database. -### The attribute table ### +

The attribute table

The attribute table contains two columns, _name_ and _bitnum_. An attribute is simply a name for a certain bit number in the attribute @@ -750,7 +902,7 @@ Read the output of for more information and a complete list of command line options to these commands. -### Blob tables ### +

Blob tables

The image, lyrics, moods and playlists tables are all blob tables. Blob tables consist of three columns each: The identifier which is @@ -777,7 +929,7 @@ Note that the images and lyrics are not interpreted at all, and also the playlist and the mood blobs are only investigated when the mood or playlist is activated with the select command. -### The score table ### +

The score table

The score table describes those audio files which are admissible for the current mood or playlist (see below). The table has two columns: @@ -803,7 +955,7 @@ terms of attributes and other type of information available in the audio file table. As an example, a mood can define a filename pattern, which is then matched against the names of audio files in the table. -### Playlists ### +

Playlists

Playlists are accommodated in the playlist table of the afs database, using the aforementioned blob format for tables. A new playlist is @@ -822,7 +974,7 @@ in descending order so that files will be selected in order. If a file could not be opened for streaming, its entry is removed from the score table (but not from the playlist). -### Moods ### +

Moods

A mood consists of a unique name and its *mood definition*, which is a set of *mood lines* containing expressions in terms of attributes @@ -897,7 +1049,7 @@ special treatment: -### List of mood_methods ### +

List of mood_methods

no_attributes_set @@ -943,7 +1095,7 @@ if the year tag is a two-digit number. In this case either 1900 or greater than 2000 plus the current year. -### Mood usage ### +

Mood usage

To create a new mood called "my_mood", write its definition into some temporary file, say "tmpfile", and add it to the mood table @@ -971,7 +1123,7 @@ if the "-a" switch is given: para ls -a -### Example mood definition ### +

Example mood definition

Suppose you have defined attributes "punk" and "rock" and want to define a mood containing only Punk-Rock songs. That is, an audio file should be @@ -1060,7 +1212,7 @@ Audio formats The following audio formats are supported by paraslash: -### MP3 ### +

MP3

Mp3, MPEG-1 Audio Layer 3, is a common audio format for audio storage, designed as part of its MPEG-1 standard. An MP3 file is made up of @@ -1070,7 +1222,7 @@ of channels. For a typical CD-audio file (sample rate of 44.1 kHz stereo), encoded with a bit rate of 128 kbit, an MP3 frame is about 400 bytes large. -### OGG/Vorbis ### +

OGG/Vorbis

OGG is a standardized audio container format, while Vorbis is an open source codec for lossy audio compression. Since Vorbis is most @@ -1080,7 +1232,7 @@ chunks called OGG pages. A typical OGG page is about 4KB large. The Vorbis codec creates variable-bitrate (VBR) data, where the bitrate may vary considerably. -### OGG/Speex ### +

OGG/Speex

Speex is an open-source speech codec that is based on CELP (Code Excited Linear Prediction) coding. It is designed for voice @@ -1090,7 +1242,7 @@ supported. As for Vorbis audio, Speex bit-streams are often stored in OGG files. As of 2012 this codec is considered obsolete since the Oppus codec, described below, surpasses its performance in all areas. -### OGG/Opus ### +

OGG/Opus

Opus is a lossy audio compression format standardized through RFC 6716 in 2012. It combines the speech-oriented SILK codec and the @@ -1099,7 +1251,7 @@ OGG/Vorbis and OGG/Speex, Opus data is usually encapsulated in OGG containers. All known software patents which cover Opus are licensed under royalty-free terms. -### AAC ### +

AAC

Advanced Audio Coding (AAC) is a standardized, lossy compression and encoding scheme for digital audio which is the default audio @@ -1107,7 +1259,7 @@ format for Apple's iPhone, iPod, iTunes. Usually MPEG-4 is used as the container format and audio files encoded with AAC have the .m4a extension. A typical AAC frame is about 700 bytes large. -### WMA ### +

WMA

Windows Media Audio (WMA) is an audio data compression technology developed by Microsoft. A WMA file is usually encapsulated in the @@ -1116,7 +1268,7 @@ how meta data about the file is to be encoded. The bit stream of WMA is composed of superframes, each containing one or more frames of 2048 samples. For 16 bit stereo a WMA superframe is about 8K large. -### FLAC ### +

FLAC

The Free Lossless Audio Codec (FLAC) compresses audio without quality loss. It gives better compression ratios than a general purpose @@ -1581,7 +1733,7 @@ they are usually placed directly after the decoding filter. Each sample is multiplied with a scaling factor (>= 1) which makes amp and compress quite expensive in terms of computing power. -### amp ### +

amp

The amp filter amplifies the audio stream by a fixed scaling factor that must be known in advance. For para_audiod this factor is derived @@ -1608,7 +1760,7 @@ To store V in the audio file table, the command is used. The reader is encouraged to write a script that performs these computations :) -### compress ### +

compress

Unlike the amplification filter, the compress filter adjusts the volume of the audio stream dynamically without prior knowledge about the peak @@ -1700,10 +1852,6 @@ emulation for backwards compatibility. This API is rather simple but also limited. For example only one application can open the device at any time. The OSS writer is activated by default on BSD Systems. -- *OSX*. Mac OS X has yet another API called CoreAudio. The OSX writer -for this API is only compiled in on such systems and is of course -the default there. - - *FILE*. The file writer allows to capture the audio stream and write the PCM data to a file on the file system rather than playing it through a sound device. It is supported on all platforms and is @@ -1833,12 +1981,14 @@ welcome. Here's a list of things you can do to help the project: - Compile and test on your favorite architecture or operating system. The code is tested only on a limited set of systems, so you will probably encounter problems when building on different systems. -- Post about about paraslash on your blog or on social networks. +- Post about paraslash on your blog or on social networks. - Build and maintain Debian/RPM packages for your favorite distribution. Note that there is no mailing list, no bug tracker and no discussion forum for paraslash. If you'd like to contribute, or have questions about contributing, send email to Andre Noll . +New releases are announced by email. If you would like to receive +these announcements, contact the author through the above address. Tools ----- @@ -1961,7 +2111,7 @@ Coding Style The preferred coding style for paraslash coincides more or less with the style of the Linux kernel. So rather than repeating what is -written [there](http://www.kernel.org/doc/Documentation/CodingStyle), +written [there](http://www.kernel.org/doc/Documentation/process/coding-style.rst), here are the most important points. - Burn the GNU coding standards. @@ -2027,14 +2177,14 @@ Appendix Network protocols ----------------- -### IP ### +

IP

The _Internet Protocol_ is the primary networking protocol used for the Internet. All protocols described below use IP as the underlying layer. Both the prevalent IPv4 and the next-generation IPv6 variant are being deployed actively worldwide. -### Connection-oriented and connectionless protocols ### +

Connection-oriented and connectionless protocols

Connectionless protocols differ from connection-oriented ones in that state associated with the sending/receiving endpoints is treated @@ -2050,7 +2200,7 @@ up-to-date internal state of the connection also in general means that the sending endpoints perform congestion control, adapting to qualitative changes of the connection medium. -### Reliability ### +

Reliability

In IP networking, packets can be lost, duplicated, or delivered out of order, and different network protocols handle these @@ -2062,7 +2212,7 @@ out-of-order. Retransmission is used to guarantee loss-free delivery. Unreliable protocols, in contrast, do not guarantee ordering or data integrity. -### Classification ### +

Classification

With these definitions the protocols which are used by paraslash for steaming audio data may be classified as follows. @@ -2073,7 +2223,7 @@ steaming audio data may be classified as follows. Below we give a short descriptions of these protocols. -### TCP ### +

TCP

The _Transmission Control Protocol_ provides reliable, ordered delivery of a stream and a classic window-based congestion control. In contrast @@ -2084,7 +2234,7 @@ extensively by many application layers. Besides HTTP (the Hypertext Transfer Protocol), also FTP (the File Transfer protocol), SMTP (Simple Mail Transfer Protocol), SSH (Secure Shell) all sit on top of TCP. -### UDP ### +

UDP

The _User Datagram Protocol_ is the simplest transport-layer protocol, built as a thin layer directly on top of IP. For this reason, it offers @@ -2095,7 +2245,7 @@ means that there is no protection against packet loss or network congestion. Error checking and correction (if at all) are performed in the application. -### DCCP ### +

DCCP

The _Datagram Congestion Control Protocol_ combines the connection-oriented state maintenance known from TCP with the @@ -2112,7 +2262,7 @@ the choice of congestion control: classic, window-based congestion control known from TCP is available as CCID-2, rate-based, "smooth" congestion control is offered as CCID-3. -### HTTP ### +

HTTP

The _Hypertext Transfer Protocol_ is an application layer protocol on top of TCP. It is spoken by web servers and is most often used @@ -2122,7 +2272,7 @@ delivery of web pages only. Being a simple request/response based protocol, the semantics of the protocol also allow the delivery of multimedia content, such as audio over http. -### Multicast ### +

Multicast

IP multicast is not really a protocol but a technique for one-to-many communication over an IP network. The challenge is to deliver