X-Git-Url: http://git.tuebingen.mpg.de/?a=blobdiff_plain;f=mp4.c;h=5ca1307f680d366c155b2e98257ba807c5a4fb92;hb=HEAD;hp=1d8af6cb20853c33a4aff5d151eb143951bd5a90;hpb=30fcea984715a12b63aab776fb3080ac1851e43a;p=paraslash.git

diff --git a/mp4.c b/mp4.c
index 1d8af6cb..fe9d4b37 100644
--- a/mp4.c
+++ b/mp4.c
@@ -5,6 +5,15 @@
  * See file COPYING.
  */
 
+/** \file mp4.c Paraslash's internal mp4 parser. */
+
+/*
+ * This is a stripped down version of the former mp4ff library which used to be
+ * part of the faad decoder project but was removed from the faad code base in
+ * 2017. The original code has been cleaned up substantially and the public API
+ * has been documented. See the git commit log for details.
+ */
+
 #include <regex.h>
 
 #include "para.h"
@@ -13,9 +22,26 @@
 #include "string.h"
 #include "mp4.h"
 
+/**
+ * The three states of the mp4 parser. The parser only loads the audio specific
+ * values and tables when it is in the second state.
+ */
+enum audio_track_state {
+	/** We haven't encountered an mp4a atom so far. */
+	ATS_INITIAL,
+	/** We have seen an mp4a atom but no subsequent trak atom yet. */
+	ATS_SEEN_MP4A,
+	/** A trak atom was seen *after* the mp4a atom. */
+	ATS_TRACK_CHANGE,
+};
+
 struct mp4_track {
-	uint16_t channelCount;
-	uint16_t sampleRate;
+	/* determines which atoms we still need to parse. */
+	enum audio_track_state state;
+
+	/* mp4a */
+	uint16_t channel_count;
+	uint16_t sample_rate;
 
 	/* stsz */
 	uint32_t stsz_sample_size;
@@ -35,15 +61,13 @@ struct mp4_track {
 	uint32_t stco_entry_count;
 	uint32_t *stco_chunk_offset;
 
-	uint32_t timeScale;
+	/* mdhd */
+	uint32_t time_scale;
 	uint64_t duration;
 };
 
-#define MAX_TRACKS 1024
-
 struct mp4 {
 	const struct mp4_callback *cb;
-	int64_t current_position;
 
 	uint64_t moov_offset;
 	uint64_t moov_size;
@@ -55,22 +79,13 @@ struct mp4 {
 	uint32_t udta_size;
 
 	uint8_t last_atom;
-	uint64_t file_size;
-
-	/* incremental track index while reading the file */
-	int32_t total_tracks;
-	/* track data */
-	struct mp4_track *track[MAX_TRACKS];
-	/* the first audio track found */
-	struct mp4_track *audio_track;
-
-	/* metadata */
+	struct mp4_track track;
 	struct mp4_metadata meta;
 };
 
 /*
- * Returns -1, 0, or 1 on errors/EOF/success. Partial reads followed by EOF or
- * read errors are treated as errors.
+ * Returns -E_MP4_READ, 0, or 1 on errors/EOF/success. Partial reads followed
+ * by EOF or read errors are treated as errors.
  */
 static int read_data(struct mp4 *f, void *data, size_t size)
 {
@@ -80,8 +95,7 @@ static int read_data(struct mp4 *f, void *data, size_t size)
 			continue;
 		/* regard EAGAIN as an error as reads should be blocking. */
 		if (ret <= 0)
-			return ret < 0? -1 : 0;
-		f->current_position += ret;
+			return ret < 0? -E_MP4_READ : 0;
 		size -= ret;
 	}
 	return 1;
@@ -92,7 +106,7 @@ static int read_int64(struct mp4 *f, uint64_t *result)
 	uint8_t data[8];
 	int ret = read_data(f, data, 8);
 
-	if (ret > 0 && result)
+	if (ret > 0)
 		*result = read_u64_be(data);
 	return ret;
 }
@@ -102,283 +116,73 @@ static int read_int32(struct mp4 *f, uint32_t *result)
 	uint8_t data[4];
 	int ret = read_data(f, data, 4);
 
-	if (ret > 0 && result)
+	if (ret > 0)
 		*result = read_u32_be(data);
 	return ret;
 }
 
-static int read_int24(struct mp4 *f, uint32_t *result)
-{
-	uint8_t data[3];
-	int ret = read_data(f, data, 3);
-
-	if (ret > 0 && result)
-		*result = read_u24_be(data);
-	return ret;
-}
-
 static int read_int16(struct mp4 *f, uint16_t *result)
 {
 	uint8_t data[2];
 	int ret = read_data(f, data, 2);
 
-	if (ret > 0 && result)
+	if (ret > 0)
 		*result = read_u16_be(data);
 	return ret;
 }
 
-static uint8_t read_int8(struct mp4 *f, uint8_t *result)
+/** \cond atom_items */
+/* A macro defining the atoms we care about. It gets expanded twice. */
+#define ATOM_ITEMS \
+	ATOM_ITEM(MOOV, 'm', 'o', 'o', 'v') /* movie (top-level container) */ \
+	ATOM_ITEM(TRAK, 't', 'r', 'a', 'k') /* container for a single track */ \
+	ATOM_ITEM(MDIA, 'm', 'd', 'i', 'a') /* media information */ \
+	ATOM_ITEM(MINF, 'm', 'i', 'n', 'f') /* extends mdia */ \
+	ATOM_ITEM(STBL, 's', 't', 'b', 'l') /* sample table container */ \
+	ATOM_ITEM(UDTA, 'u', 'd', 't', 'a') /* user data */ \
+	ATOM_ITEM(ILST, 'i', 'l', 's', 't') /* iTunes Metadata list */ \
+	ATOM_ITEM(ARTIST, 0xa9, 'A', 'R', 'T') /* artist */ \
+	ATOM_ITEM(TITLE, 0xa9, 'n', 'a', 'm') /* title */ \
+	ATOM_ITEM(ALBUM, 0xa9, 'a', 'l', 'b') /* album */ \
+	ATOM_ITEM(DATE, 0xa9, 'd', 'a', 'y') /* date */ \
+	ATOM_ITEM(COMMENT, 0xa9, 'c', 'm', 't') /* comment */ \
+	ATOM_ITEM(MDHD, 'm', 'd', 'h', 'd') /* track header */ \
+	ATOM_ITEM(STSD, 's', 't', 's', 'd') /* sample description box */ \
+	ATOM_ITEM(STTS, 's', 't', 't', 's') /* time to sample box */ \
+	ATOM_ITEM(STSZ, 's', 't', 's', 'z') /* sample size box */ \
+	ATOM_ITEM(STCO, 's', 't', 'c', 'o') /* chunk offset box */ \
+	ATOM_ITEM(STSC, 's', 't', 's', 'c') /* sample to chunk box */ \
+	ATOM_ITEM(MP4A, 'm', 'p', '4', 'a') /* mp4 audio */ \
+	ATOM_ITEM(META, 'm', 'e', 't', 'a') /* iTunes Metadata box */ \
+	ATOM_ITEM(DATA, 'd', 'a', 't', 'a') /* iTunes Metadata data box */ \
+
+/** \endcond atom_items */
+
+/** For the C enumeration we concatenate ATOM_ with the first argument. */
+#define ATOM_ITEM(_name, a, b, c, d) ATOM_ ## _name,
+/** The enumeration of interesting atoms. */
+enum atom {ATOM_ITEMS};
+#undef ATOM_ITEM
+
+/** A cpp version of read_u32_be(). */
+#define ATOM_VALUE(a, b, c, d) ((a << 24) + (b << 16) + (c << 8) + d)
+
+static uint8_t atom_name_to_type(uint8_t *p)
 {
-	uint8_t data[1];
-	int ret = read_data(f, data, 1);
-
-	if (ret > 0 && result)
-		*result = data[0];
-	return ret;
-}
-
-static bool atom_compare(int8_t a1, int8_t b1, int8_t c1, int8_t d1,
-		int8_t a2, int8_t b2, int8_t c2, int8_t d2)
-{
-	return a1 == a2 && b1 == b2 && c1 == c2 && d1 == d2;
-}
-
-enum atoms {
-	/* atoms with subatoms */
-	ATOM_MOOV = 1,
-	ATOM_TRAK = 2,
-	ATOM_EDTS = 3,
-	ATOM_MDIA = 4,
-	ATOM_MINF = 5,
-	ATOM_STBL = 6,
-	ATOM_UDTA = 7,
-	ATOM_ILST = 8, /* iTunes Metadata list */
-	ATOM_TITLE = 9,
-	ATOM_ARTIST = 10,
-	ATOM_WRITER = 11,
-	ATOM_ALBUM = 12,
-	ATOM_DATE = 13,
-	ATOM_TOOL = 14,
-	ATOM_COMMENT = 15,
-	ATOM_GENRE1 = 16,
-	ATOM_TRACK = 17,
-	ATOM_DISC = 18,
-	ATOM_COMPILATION = 19,
-	ATOM_GENRE2 = 20,
-	ATOM_TEMPO = 21,
-	ATOM_COVER = 22,
-	ATOM_DRMS = 23,
-	ATOM_SINF = 24,
-	ATOM_SCHI = 25,
-
-	SUBATOMIC = 128,
-
-	/* atoms without subatoms */
-	ATOM_FTYP = 129,
-	ATOM_MDAT = 130,
-	ATOM_MVHD = 131,
-	ATOM_TKHD = 132,
-	ATOM_TREF = 133,
-	ATOM_MDHD = 134, /* track header */
-	ATOM_VMHD = 135,
-	ATOM_SMHD = 136,
-	ATOM_HMHD = 137,
-	ATOM_STSD = 138, /* sample description box */
-	ATOM_STTS = 139, /* time to sample box */
-	ATOM_STSZ = 140, /* sample size box */
-	ATOM_STZ2 = 141,
-	ATOM_STCO = 142, /* chunk offset box */
-	ATOM_STSC = 143, /* sample to chunk box */
-	ATOM_MP4A = 144,
-	ATOM_MP4V = 145,
-	ATOM_MP4S = 146,
-	ATOM_ESDS = 147,
-	ATOM_META = 148, /* iTunes Metadata box */
-	ATOM_NAME = 149, /* iTunes Metadata name box */
-	ATOM_DATA = 150, /* iTunes Metadata data box */
-	ATOM_CTTS = 151,
-	ATOM_FRMA = 152,
-	ATOM_IVIV = 153,
-	ATOM_PRIV = 154,
-	ATOM_USER = 155,
-	ATOM_KEY = 156,
-	ATOM_ALBUM_ARTIST = 157,
-	ATOM_CONTENTGROUP = 158,
-	ATOM_LYRICS = 159,
-	ATOM_DESCRIPTION = 160,
-	ATOM_NETWORK = 161,
-	ATOM_SHOW = 162,
-	ATOM_EPISODENAME = 163,
-	ATOM_SORTTITLE = 164,
-	ATOM_SORTALBUM = 165,
-	ATOM_SORTARTIST = 166,
-	ATOM_SORTALBUMARTIST = 167,
-	ATOM_SORTWRITER = 168,
-	ATOM_SORTSHOW = 169,
-	ATOM_SEASON = 170,
-	ATOM_EPISODE = 171,
-	ATOM_PODCAST = 172,
-
-	ATOM_UNKNOWN = 255
-};
-
-#define ATOM_FREE ATOM_UNKNOWN
-#define ATOM_SKIP ATOM_UNKNOWN
-
-#define COPYRIGHT_SYMBOL ((int8_t)0xA9)
-
-static uint8_t atom_name_to_type(int8_t a, int8_t b, int8_t c, int8_t d)
-{
-	if (a == 'm') {
-		if (atom_compare(a, b, c, d, 'm', 'o', 'o', 'v'))
-			return ATOM_MOOV;
-		else if (atom_compare(a, b, c, d, 'm', 'i', 'n', 'f'))
-			return ATOM_MINF;
-		else if (atom_compare(a, b, c, d, 'm', 'd', 'i', 'a'))
-			return ATOM_MDIA;
-		else if (atom_compare(a, b, c, d, 'm', 'd', 'a', 't'))
-			return ATOM_MDAT;
-		else if (atom_compare(a, b, c, d, 'm', 'd', 'h', 'd'))
-			return ATOM_MDHD;
-		else if (atom_compare(a, b, c, d, 'm', 'v', 'h', 'd'))
-			return ATOM_MVHD;
-		else if (atom_compare(a, b, c, d, 'm', 'p', '4', 'a'))
-			return ATOM_MP4A;
-		else if (atom_compare(a, b, c, d, 'm', 'p', '4', 'v'))
-			return ATOM_MP4V;
-		else if (atom_compare(a, b, c, d, 'm', 'p', '4', 's'))
-			return ATOM_MP4S;
-		else if (atom_compare(a, b, c, d, 'm', 'e', 't', 'a'))
-			return ATOM_META;
-	} else if (a == 't') {
-		if (atom_compare(a, b, c, d, 't', 'r', 'a', 'k'))
-			return ATOM_TRAK;
-		else if (atom_compare(a, b, c, d, 't', 'k', 'h', 'd'))
-			return ATOM_TKHD;
-		else if (atom_compare(a, b, c, d, 't', 'r', 'e', 'f'))
-			return ATOM_TREF;
-		else if (atom_compare(a, b, c, d, 't', 'r', 'k', 'n'))
-			return ATOM_TRACK;
-		else if (atom_compare(a, b, c, d, 't', 'm', 'p', 'o'))
-			return ATOM_TEMPO;
-		else if (atom_compare(a, b, c, d, 't', 'v', 'n', 'n'))
-			return ATOM_NETWORK;
-		else if (atom_compare(a, b, c, d, 't', 'v', 's', 'h'))
-			return ATOM_SHOW;
-		else if (atom_compare(a, b, c, d, 't', 'v', 'e', 'n'))
-			return ATOM_EPISODENAME;
-		else if (atom_compare(a, b, c, d, 't', 'v', 's', 'n'))
-			return ATOM_SEASON;
-		else if (atom_compare(a, b, c, d, 't', 'v', 'e', 's'))
-			return ATOM_EPISODE;
-	} else if (a == 's') {
-		if (atom_compare(a, b, c, d, 's', 't', 'b', 'l'))
-			return ATOM_STBL;
-		else if (atom_compare(a, b, c, d, 's', 'm', 'h', 'd'))
-			return ATOM_SMHD;
-		else if (atom_compare(a, b, c, d, 's', 't', 's', 'd'))
-			return ATOM_STSD;
-		else if (atom_compare(a, b, c, d, 's', 't', 't', 's'))
-			return ATOM_STTS;
-		else if (atom_compare(a, b, c, d, 's', 't', 'c', 'o'))
-			return ATOM_STCO;
-		else if (atom_compare(a, b, c, d, 's', 't', 's', 'c'))
-			return ATOM_STSC;
-		else if (atom_compare(a, b, c, d, 's', 't', 's', 'z'))
-			return ATOM_STSZ;
-		else if (atom_compare(a, b, c, d, 's', 't', 'z', '2'))
-			return ATOM_STZ2;
-		else if (atom_compare(a, b, c, d, 's', 'k', 'i', 'p'))
-			return ATOM_SKIP;
-		else if (atom_compare(a, b, c, d, 's', 'i', 'n', 'f'))
-			return ATOM_SINF;
-		else if (atom_compare(a, b, c, d, 's', 'c', 'h', 'i'))
-			return ATOM_SCHI;
-		else if (atom_compare(a, b, c, d, 's', 'o', 'n', 'm'))
-			return ATOM_SORTTITLE;
-		else if (atom_compare(a, b, c, d, 's', 'o', 'a', 'l'))
-			return ATOM_SORTALBUM;
-		else if (atom_compare(a, b, c, d, 's', 'o', 'a', 'r'))
-			return ATOM_SORTARTIST;
-		else if (atom_compare(a, b, c, d, 's', 'o', 'a', 'a'))
-			return ATOM_SORTALBUMARTIST;
-		else if (atom_compare(a, b, c, d, 's', 'o', 'c', 'o'))
-			return ATOM_SORTWRITER;
-		else if (atom_compare(a, b, c, d, 's', 'o', 's', 'n'))
-			return ATOM_SORTSHOW;
-	} else if (a == COPYRIGHT_SYMBOL) {
-		if (atom_compare(a, b, c, d, COPYRIGHT_SYMBOL, 'n', 'a', 'm'))
-			return ATOM_TITLE;
-		else if (atom_compare(a, b, c, d, COPYRIGHT_SYMBOL, 'A', 'R', 'T'))
-			return ATOM_ARTIST;
-		else if (atom_compare(a, b, c, d, COPYRIGHT_SYMBOL, 'w', 'r', 't'))
-			return ATOM_WRITER;
-		else if (atom_compare(a, b, c, d, COPYRIGHT_SYMBOL, 'a', 'l', 'b'))
-			return ATOM_ALBUM;
-		else if (atom_compare(a, b, c, d, COPYRIGHT_SYMBOL, 'd', 'a', 'y'))
-			return ATOM_DATE;
-		else if (atom_compare(a, b, c, d, COPYRIGHT_SYMBOL, 't', 'o', 'o'))
-			return ATOM_TOOL;
-		else if (atom_compare(a, b, c, d, COPYRIGHT_SYMBOL, 'c', 'm', 't'))
-			return ATOM_COMMENT;
-		else if (atom_compare(a, b, c, d, COPYRIGHT_SYMBOL, 'g', 'e', 'n'))
-			return ATOM_GENRE1;
-		else if (atom_compare(a, b, c, d, COPYRIGHT_SYMBOL, 'g', 'r', 'p'))
-			return ATOM_CONTENTGROUP;
-		else if (atom_compare(a, b, c, d, COPYRIGHT_SYMBOL, 'l', 'y', 'r'))
-			return ATOM_LYRICS;
-	}
-
-	if (atom_compare(a, b, c, d, 'e', 'd', 't', 's'))
-		return ATOM_EDTS;
-	else if (atom_compare(a, b, c, d, 'e', 's', 'd', 's'))
-		return ATOM_ESDS;
-	else if (atom_compare(a, b, c, d, 'f', 't', 'y', 'p'))
-		return ATOM_FTYP;
-	else if (atom_compare(a, b, c, d, 'f', 'r', 'e', 'e'))
-		return ATOM_FREE;
-	else if (atom_compare(a, b, c, d, 'h', 'm', 'h', 'd'))
-		return ATOM_HMHD;
-	else if (atom_compare(a, b, c, d, 'v', 'm', 'h', 'd'))
-		return ATOM_VMHD;
-	else if (atom_compare(a, b, c, d, 'u', 'd', 't', 'a'))
-		return ATOM_UDTA;
-	else if (atom_compare(a, b, c, d, 'i', 'l', 's', 't'))
-		return ATOM_ILST;
-	else if (atom_compare(a, b, c, d, 'n', 'a', 'm', 'e'))
-		return ATOM_NAME;
-	else if (atom_compare(a, b, c, d, 'd', 'a', 't', 'a'))
-		return ATOM_DATA;
-	else if (atom_compare(a, b, c, d, 'd', 'i', 's', 'k'))
-		return ATOM_DISC;
-	else if (atom_compare(a, b, c, d, 'g', 'n', 'r', 'e'))
-		return ATOM_GENRE2;
-	else if (atom_compare(a, b, c, d, 'c', 'o', 'v', 'r'))
-		return ATOM_COVER;
-	else if (atom_compare(a, b, c, d, 'c', 'p', 'i', 'l'))
-		return ATOM_COMPILATION;
-	else if (atom_compare(a, b, c, d, 'c', 't', 't', 's'))
-		return ATOM_CTTS;
-	else if (atom_compare(a, b, c, d, 'd', 'r', 'm', 's'))
-		return ATOM_DRMS;
-	else if (atom_compare(a, b, c, d, 'f', 'r', 'm', 'a'))
-		return ATOM_FRMA;
-	else if (atom_compare(a, b, c, d, 'p', 'r', 'i', 'v'))
-		return ATOM_PRIV;
-	else if (atom_compare(a, b, c, d, 'i', 'v', 'i', 'v'))
-		return ATOM_IVIV;
-	else if (atom_compare(a, b, c, d, 'u', 's', 'e', 'r'))
-		return ATOM_USER;
-	else if (atom_compare(a, b, c, d, 'k', 'e', 'y', ' '))
-		return ATOM_KEY;
-	else if (atom_compare(a, b, c, d, 'a', 'A', 'R', 'T'))
-		return ATOM_ALBUM_ARTIST;
-	else if (atom_compare(a, b, c, d, 'd', 'e', 's', 'c'))
-		return ATOM_DESCRIPTION;
-	else if (atom_compare(a, b, c, d, 'p', 'c', 's', 't'))
-		return ATOM_PODCAST;
-	else
-		return ATOM_UNKNOWN;
+	/** Expands to an instance of the following unnamed structure. */
+	#define ATOM_ITEM(_name, a, b, c, d) \
+		{.name = # _name, .val = ATOM_VALUE(a, b, c, d)},
+	static const struct {
+		const char *name;
+		uint32_t val;
+	} atom_table[] = {ATOM_ITEMS};
+	#undef ATOM_ITEM
+	uint32_t val = read_u32_be(p);
+
+	for (uint8_t n = 0; n < ARRAY_SIZE(atom_table); n++)
+		if (val == atom_table[n].val)
+			return n;
+	return 255;
 }
 
 /* read atom header, atom size is returned with header included. */
@@ -387,7 +191,7 @@ static int atom_read_header(struct mp4 *f, uint8_t *atom_type,
 {
 	uint32_t size;
 	int ret;
-	int8_t atom_header[8];
+	uint8_t atom_header[8];
 
 	ret = read_data(f, atom_header, 8);
 	if (ret <= 0)
@@ -402,42 +206,35 @@ static int atom_read_header(struct mp4 *f, uint8_t *atom_type,
 	} else {
 		if (header_size)
 			*header_size = 8;
-		if (atom_size)
-			*atom_size = size;
+		*atom_size = size;
 	}
-	*atom_type = atom_name_to_type(atom_header[4], atom_header[5],
-		atom_header[6], atom_header[7]);
+	*atom_type = atom_name_to_type(atom_header + 4);
 	return 1;
 }
 
-static int64_t get_position(const struct mp4 *f)
+static off_t get_position(const struct mp4 *f)
 {
-	return f->current_position;
+	return f->cb->seek(f->cb->user_data, 0, SEEK_CUR);
 }
 
-static int32_t set_position(struct mp4 *f, int64_t position)
+static void set_position(struct mp4 *f, off_t position)
 {
-	f->cb->seek(f->cb->user_data, position);
-	f->current_position = position;
+	f->cb->seek(f->cb->user_data, position, SEEK_SET);
+}
 
-	return 0;
+static void skip_bytes(struct mp4 *f, off_t num_skip)
+{
+	f->cb->seek(f->cb->user_data, num_skip, SEEK_CUR);
 }
 
 static int read_stsz(struct mp4 *f)
 {
 	int ret;
-	int32_t i;
-	struct mp4_track *t;
+	struct mp4_track *t = &f->track;
 
-	if (f->total_tracks == 0)
-		return -1;
-	t = f->track[f->total_tracks - 1];
-	ret = read_int8(f, NULL); /* version */
-	if (ret <= 0)
-		return ret;
-	ret = read_int24(f, NULL); /* flags */
-	if (ret <= 0)
-		return ret;
+	if (t->state != ATS_SEEN_MP4A || t->stsz_table)
+		return 1;
+	skip_bytes(f, 4); /* version (1), flags (3) */
 	ret = read_int32(f, &t->stsz_sample_size);
 	if (ret <= 0)
 		return ret;
@@ -446,9 +243,9 @@ static int read_stsz(struct mp4 *f)
 		return ret;
 	if (t->stsz_sample_size != 0)
 		return 1;
-	t->stsz_table = para_malloc(t->stsz_sample_count * sizeof(int32_t));
-	for (i = 0; i < t->stsz_sample_count; i++) {
-		ret = read_int32(f, &t->stsz_table[i]);
+	t->stsz_table = arr_alloc(t->stsz_sample_count, sizeof(int32_t));
+	for (uint32_t n = 0; n < t->stsz_sample_count; n++) {
+		ret = read_int32(f, &t->stsz_table[n]);
 		if (ret <= 0)
 			return ret;
 	}
@@ -458,32 +255,20 @@ static int read_stsz(struct mp4 *f)
 static int read_stts(struct mp4 *f)
 {
 	int ret;
-	int32_t i;
-	struct mp4_track *t;
+	struct mp4_track *t = &f->track;
 
-	if (f->total_tracks == 0)
-		return -1;
-	t = f->track[f->total_tracks - 1];
-	if (t->stts_entry_count)
-		return 0;
-	ret = read_int8(f, NULL); /* version */
-	if (ret <= 0)
-		return ret;
-	ret = read_int24(f, NULL); /* flags */
-	if (ret <= 0)
-		return ret;
+	if (t->state != ATS_SEEN_MP4A || t->stts_sample_count)
+		return 1;
+	skip_bytes(f, 4); /* version (1), flags (3) */
 	ret = read_int32(f, &t->stts_entry_count);
 	if (ret <= 0)
 		return ret;
-	t->stts_sample_count = para_malloc(t->stts_entry_count
-		* sizeof(int32_t));
-	for (i = 0; i < t->stts_entry_count; i++) {
-		ret = read_int32(f, &t->stts_sample_count[i]);
-		if (ret <= 0)
-			return ret;
-		ret = read_int32(f, NULL); /* sample delta */
+	t->stts_sample_count = arr_alloc(t->stts_entry_count, sizeof(int32_t));
+	for (uint32_t n = 0; n < t->stts_entry_count; n++) {
+		ret = read_int32(f, &t->stts_sample_count[n]);
 		if (ret <= 0)
 			return ret;
+		skip_bytes(f, 4); /* sample delta */
 	}
 	return 1;
 }
@@ -491,35 +276,27 @@ static int read_stts(struct mp4 *f)
 static int read_stsc(struct mp4 *f)
 {
 	int ret;
-	int32_t i;
-	struct mp4_track *t;
+	struct mp4_track *t = &f->track;
 
-	if (f->total_tracks == 0)
-		return -1;
-	t = f->track[f->total_tracks - 1];
-
-	ret = read_int8(f, NULL); /* version */
-	if (ret <= 0)
-		return ret;
-	ret = read_int24(f, NULL); /* flags */
-	if (ret <= 0)
-		return ret;
+	if (t->state != ATS_SEEN_MP4A)
+		return 1;
+	if (t->stsc_first_chunk || t->stsc_samples_per_chunk)
+		return 1;
+	skip_bytes(f, 4); /* version (1), flags (3) */
 	ret = read_int32(f, &t->stsc_entry_count);
 	if (ret <= 0)
 		return ret;
-	t->stsc_first_chunk = para_malloc(t->stsc_entry_count * sizeof(int32_t));
-	t->stsc_samples_per_chunk = para_malloc(t->stsc_entry_count
-		* sizeof (int32_t));
-	for (i = 0; i < t->stsc_entry_count; i++) {
-		ret = read_int32(f, &t->stsc_first_chunk[i]);
+	t->stsc_first_chunk = arr_alloc(t->stsc_entry_count, sizeof(int32_t));
+	t->stsc_samples_per_chunk = arr_alloc(t->stsc_entry_count,
+		sizeof (int32_t));
+	for (uint32_t n = 0; n < t->stsc_entry_count; n++) {
+		ret = read_int32(f, &t->stsc_first_chunk[n]);
 		if (ret <= 0)
 			return ret;
-		ret = read_int32(f, &t->stsc_samples_per_chunk[i]);
-		if (ret <= 0)
-			return ret;
-		ret = read_int32(f, NULL); /* sample desc index */
+		ret = read_int32(f, &t->stsc_samples_per_chunk[n]);
 		if (ret <= 0)
 			return ret;
+		skip_bytes(f, 4); /* sample desc index */
 	}
 	return 1;
 }
@@ -527,90 +304,35 @@ static int read_stsc(struct mp4 *f)
 static int read_stco(struct mp4 *f)
 {
 	int ret;
-	int32_t i;
-	struct mp4_track *t;
+	struct mp4_track *t = &f->track;
 
-	if (f->total_tracks == 0)
-		return -1;
-	t = f->track[f->total_tracks - 1];
-
-	ret = read_int8(f, NULL); /* version */
-	if (ret <= 0)
-		return ret;
-	ret = read_int24(f, NULL); /* flags */
-	if (ret <= 0)
-		return ret;
+	if (t->state != ATS_SEEN_MP4A || t->stco_chunk_offset)
+		return 1;
+	skip_bytes(f, 4); /* version (1), flags (3) */
 	ret = read_int32(f, &t->stco_entry_count);
 	if (ret <= 0)
 		return ret;
-	t->stco_chunk_offset = para_malloc(t->stco_entry_count
-		* sizeof(int32_t));
-	for (i = 0; i < t->stco_entry_count; i++) {
-		ret = read_int32(f, &t->stco_chunk_offset[i]);
+	t->stco_chunk_offset = arr_alloc(t->stco_entry_count, sizeof(int32_t));
+	for (uint32_t n = 0; n < t->stco_entry_count; n++) {
+		ret = read_int32(f, &t->stco_chunk_offset[n]);
 		if (ret <= 0)
 			return ret;
 	}
 	return 1;
 }
 
-static int read_mp4a(struct mp4 *f)
-{
-	int ret;
-	int32_t i;
-	struct mp4_track *t;
-
-	if (f->total_tracks == 0)
-		return -1;
-	t = f->track[f->total_tracks - 1];
-
-	for (i = 0; i < 6; i++) {
-		ret = read_int8(f, NULL); /* reserved */
-		if (ret <= 0)
-			return ret;
-	}
-	ret = read_int16(f, NULL); /* data_reference_index */
-	if (ret <= 0)
-		return ret;
-	ret = read_int32(f, NULL); /* reserved */
-	if (ret <= 0)
-		return ret;
-	ret = read_int32(f, NULL); /* reserved */
-	if (ret <= 0)
-		return ret;
-	ret = read_int16(f, &t->channelCount);
-	if (ret <= 0)
-		return ret;
-	ret = read_int16(f, NULL);
-	if (ret <= 0)
-		return ret;
-	ret = read_int16(f, NULL);
-	if (ret <= 0)
-		return ret;
-	ret = read_int16(f, NULL);
-	if (ret <= 0)
-		return ret;
-	return read_int16(f, &t->sampleRate);
-}
-
 static int read_stsd(struct mp4 *f)
 {
 	int ret;
-	uint32_t i, entry_count;
-	struct mp4_track *t;
+	uint32_t entry_count;
 
-	if (f->total_tracks == 0)
-		return -1;
-	t = f->track[f->total_tracks - 1];
-	ret = read_int8(f, NULL); /* version */
-	if (ret <= 0)
-		return ret;
-	ret = read_int24(f, NULL); /* flags */
-	if (ret <= 0)
-		return ret;
+	if (f->track.state != ATS_INITIAL)
+		return 1;
+	skip_bytes(f, 4); /* version (1), flags (3) */
 	ret = read_int32(f, &entry_count);
 	if (ret <= 0)
 		return ret;
-	for (i = 0; i < entry_count; i++) {
+	for (uint32_t n = 0; n < entry_count; n++) {
 		uint64_t skip = get_position(f);
 		uint64_t size;
 		uint8_t atom_type = 0;
@@ -618,9 +340,17 @@ static int read_stsd(struct mp4 *f)
 		if (ret <= 0)
 			return ret;
 		skip += size;
-		if (!f->audio_track && atom_type == ATOM_MP4A) {
-			f->audio_track = t;
-			read_mp4a(f);
+		if (atom_type == ATOM_MP4A) {
+			f->track.state = ATS_SEEN_MP4A;
+			/* reserved (6), data reference index (2), reserved (8) */
+			skip_bytes(f, 16);
+			ret = read_int16(f, &f->track.channel_count);
+			if (ret <= 0)
+				return ret;
+			skip_bytes(f, 6);
+			ret = read_int16(f, &f->track.sample_rate);
+			if (ret <= 0)
+				return ret;
 		}
 		set_position(f, skip);
 	}
@@ -661,34 +391,25 @@ static int parse_tag(struct mp4 *f, uint8_t parent, int32_t size)
 		destpos = get_position(f) + subsize - header_size;
 		if (atom_type != ATOM_DATA)
 			continue;
-		ret = read_int8(f, NULL); /* version */
-		if (ret <= 0)
-			goto fail;
-		ret = read_int24(f, NULL); /* flags */
-		if (ret <= 0)
-			goto fail;
-		ret = read_int32(f, NULL); /* reserved */
-		if (ret <= 0)
-			goto fail;
-		ret = -ERRNO_TO_PARA_ERROR(EINVAL);
+		skip_bytes(f, 8); /* version (1), flags (3), reserved (4) */
+		ret = -E_MP4_CORRUPT;
 		if (subsize < header_size + 8 || subsize > UINT_MAX)
 			goto fail;
 		len = subsize - (header_size + 8);
 		free(value);
-		value = para_malloc(len + 1);
+		value = alloc(len + 1);
 		ret = read_data(f, value, len);
 		if (ret <= 0)
 			goto fail;
 		value[len] = '\0';
 	}
 	if (!value)
-		return -ERRNO_TO_PARA_ERROR(EINVAL);
+		return -E_MP4_CORRUPT;
 	f->meta.tags = para_realloc(f->meta.tags, (f->meta.count + 1)
 		* sizeof(struct mp4_tag));
 	tag = f->meta.tags + f->meta.count;
 	tag->item = para_strdup(get_metadata_name(parent));
 	tag->value = value;
-	tag->len = len;
 	f->meta.count++;
 	return 1;
 fail:
@@ -700,38 +421,26 @@ static int read_mdhd(struct mp4 *f)
 {
 	int ret;
 	uint32_t version;
-	struct mp4_track *t;
-
-	if (f->total_tracks == 0)
-		return -1;
-	t = f->track[f->total_tracks - 1];
+	struct mp4_track *t = &f->track;
 
+	if (t->state != ATS_INITIAL)
+		return 1;
 	ret = read_int32(f, &version);
 	if (ret <= 0)
 		return ret;
 	if (version == 1) {
-		ret = read_int64(f, NULL); /* creation-time */
-		if (ret <= 0)
-			return ret;
-		ret = read_int64(f, NULL); /* modification-time */
-		if (ret <= 0)
-			return ret;
-		ret = read_int32(f, &t->timeScale);
+		skip_bytes(f, 16); /* creation time (8), modification time (8) */
+		ret = read_int32(f, &t->time_scale);
 		if (ret <= 0)
 			return ret;
 		ret = read_int64(f, &t->duration);
 		if (ret <= 0)
 			return ret;
-	} else { //version == 0
+	} else { /* version == 0 */
 		uint32_t temp;
 
-		ret = read_int32(f, NULL); /* creation-time */
-		if (ret <= 0)
-			return ret;
-		ret = read_int32(f, NULL); /* modification-time */
-		if (ret <= 0)
-			return ret;
-		ret = read_int32(f, &t->timeScale);
+		skip_bytes(f, 8); /* creation time (4), modification time (4) */
+		ret = read_int32(f, &t->time_scale);
 		if (ret <= 0)
 			return ret;
 		ret = read_int32(f, &temp);
@@ -740,16 +449,11 @@ static int read_mdhd(struct mp4 *f)
 		t->duration = (temp == (uint32_t) (-1))?
 			(uint64_t) (-1) : (uint64_t) (temp);
 	}
-	ret = read_int16(f, NULL);
-	if (ret <= 0)
-		return ret;
-	ret = read_int16(f, NULL);
-	if (ret <= 0)
-		return ret;
+	skip_bytes(f, 4);
 	return 1;
 }
 
-static int32_t read_ilst(struct mp4 *f, int32_t size)
+static int read_ilst(struct mp4 *f, int32_t size)
 {
 	int ret;
 	uint64_t sumsize = 0;
@@ -778,19 +482,14 @@ static int32_t read_ilst(struct mp4 *f, int32_t size)
 	return 1;
 }
 
-static int32_t read_meta(struct mp4 *f, uint64_t size)
+static int read_meta(struct mp4 *f, uint64_t size)
 {
 	int ret;
 	uint64_t subsize, sumsize = 0;
 	uint8_t atom_type;
 	uint8_t header_size = 0;
 
-	ret = read_int8(f, NULL); /* version */
-	if (ret <= 0)
-		return ret;
-	ret = read_int24(f, NULL); /* flags */
-	if (ret <= 0)
-		return ret;
+	skip_bytes(f, 4); /* version (1), flags (3) */
 	while (sumsize < (size - (header_size + 4))) {
 		ret = atom_read_header(f, &atom_type, &header_size, &subsize);
 		if (ret <= 0)
@@ -810,29 +509,6 @@ static int32_t read_meta(struct mp4 *f, uint64_t size)
 	return 1;
 }
 
-static int parse_leaf_atom(struct mp4 *f, uint64_t size, uint8_t header_size,
-		uint8_t atom_type)
-{
-	uint64_t dest_position = get_position(f) + size - 8;
-	int ret = 1; /* return success for atoms we don't care about */
-
-	switch (atom_type) {
-	case ATOM_STSZ: ret = read_stsz(f); break;
-	case ATOM_STTS: ret = read_stts(f); break;
-	case ATOM_STSC: ret = read_stsc(f); break;
-	case ATOM_STCO: ret = read_stco(f); break;
-	case ATOM_STSD: ret = read_stsd(f); break;
-	case ATOM_MDHD: ret = read_mdhd(f); break;
-	case ATOM_META:
-		f->meta_offset = get_position(f) - header_size;
-		f->meta_size = size;
-		ret = read_meta(f, size);
-		break;
-	}
-	set_position(f, dest_position);
-	return ret;
-}
-
 static bool need_atom(uint8_t atom_type, bool meta_only)
 {
 	/* these are needed in any case */
@@ -865,52 +541,79 @@ static bool need_atom(uint8_t atom_type, bool meta_only)
 static int parse_sub_atoms(struct mp4 *f, uint64_t total_size, bool meta_only)
 {
 	int ret;
-	uint64_t size;
-	uint8_t atom_type = 0;
-	uint64_t counted_size = 0;
-	uint8_t header_size = 0;
+	uint64_t dest, size, end = get_position(f) + total_size;
 
-	while (counted_size < total_size) {
+	for (dest = get_position(f); dest < end; set_position(f, dest)) {
+		uint8_t header_size, atom_type;
 		ret = atom_read_header(f, &atom_type, &header_size, &size);
 		if (ret <= 0)
 			return ret;
 		if (size == 0)
-			return -1;
-		counted_size += size;
-		if (atom_type == ATOM_TRAK) {
-			if (f->total_tracks >= MAX_TRACKS)
-				return -1;
-			f->total_tracks++;
-			f->track[f->total_tracks - 1] = para_calloc(
-				sizeof(struct mp4_track));
-		} else if (atom_type == ATOM_UDTA) {
+			return -E_MP4_CORRUPT;
+		dest = get_position(f) + size - header_size;
+		if (atom_type == ATOM_TRAK && f->track.state == ATS_SEEN_MP4A) {
+			f->track.state = ATS_TRACK_CHANGE;
+			continue;
+		}
+		if (atom_type == ATOM_UDTA) {
 			f->udta_offset = get_position(f) - header_size;
 			f->udta_size = size;
 		}
-		if (!need_atom(atom_type, meta_only)) {
-			set_position(f, get_position(f) + size - header_size);
+		if (!need_atom(atom_type, meta_only))
 			continue;
-		}
-		if (atom_type < SUBATOMIC) /* atom contains subatoms */
+		switch (atom_type) {
+		case ATOM_STSZ: ret = read_stsz(f); break;
+		case ATOM_STTS: ret = read_stts(f); break;
+		case ATOM_STSC: ret = read_stsc(f); break;
+		case ATOM_STCO: ret = read_stco(f); break;
+		case ATOM_STSD: ret = read_stsd(f); break;
+		case ATOM_MDHD: ret = read_mdhd(f); break;
+		case ATOM_META:
+			f->meta_offset = get_position(f) - header_size;
+			f->meta_size = size;
+			ret = read_meta(f, size);
+			break;
+		default:
 			ret = parse_sub_atoms(f, size - header_size, meta_only);
-		else
-			ret = parse_leaf_atom(f, size, header_size, atom_type);
+		}
 		if (ret <= 0)
 			return ret;
 	}
 	return 1;
 }
 
+/**
+ * Deallocate all resources associated with an mp4 file handle.
+ *
+ * \param f File handle returned by \ref mp4_open() or \ref mp4_open_meta().
+ *
+ * This frees the metadata items and various tables which were allocated when
+ * the file was opened. The given file handle must not be NULL.
+ */
+void mp4_close(struct mp4 *f)
+{
+	free(f->track.stsz_table);
+	free(f->track.stts_sample_count);
+	free(f->track.stsc_first_chunk);
+	free(f->track.stsc_samples_per_chunk);
+	free(f->track.stco_chunk_offset);
+	for (uint32_t n = 0; n < f->meta.count; n++) {
+		free(f->meta.tags[n].item);
+		free(f->meta.tags[n].value);
+	}
+	free(f->meta.tags);
+	free(f);
+}
+
 static int open_file(const struct mp4_callback *cb, bool meta_only, struct mp4 **result)
 {
 	int ret;
 	uint64_t size;
 	uint8_t atom_type, header_size;
-	struct mp4 *f = para_calloc(sizeof(*f));
+	struct mp4 *f = zalloc(sizeof(*f));
 
 	f->cb = cb;
 	while ((ret = atom_read_header(f, &atom_type, &header_size, &size)) > 0) {
-		f->file_size += size;
 		f->last_atom = atom_type;
 		if (atom_type != ATOM_MOOV || size <= header_size) { /* skip */
 			set_position(f, get_position(f) + size - header_size);
@@ -922,62 +625,79 @@ static int open_file(const struct mp4_callback *cb, bool meta_only, struct mp4 *
 		if (ret <= 0)
 			break;
 	}
-	if (ret < 0) {
-		ret = -E_MP4_OPEN;
+	if (ret < 0)
 		goto fail;
-	}
 	ret = -E_MP4_TRACK;
-	if (!f->audio_track)
+	if (f->track.channel_count == 0)
+		goto fail;
+	ret = -E_MP4_BAD_SAMPLERATE;
+	if (f->track.sample_rate == 0)
+		goto fail;
+	ret = -E_MP4_MISSING_ATOM;
+	if (f->udta_size == 0 || f->meta_size == 0 || f->ilst_size == 0)
 		goto fail;
 	*result = f;
 	return 1;
 fail:
 	*result = NULL;
-	free(f);
+	mp4_close(f);
 	return ret;
 }
 
-int mp4_open_read(const struct mp4_callback *cb, struct mp4 **result)
+/**
+ * Read the audio track and the metadata of an mp4 file.
+ *
+ * \param cb Only the ->read() and ->seek() methods need to be supplied.
+ * \param result Initialized to a non-NULL pointer iff the function succeeds.
+ *
+ * This detects and parses the first audio track and the metadata information
+ * of the mp4 file. Various error checks are performed after the mp4 atoms have
+ * been parsed successfully.
+ *
+ * This function does not modify the file. However, if the caller intents to
+ * update the metadata later, the ->write() and ->truncate() methods must be
+ * supplied in the callback structure.
+ *
+ * \return Standard. Several errors are possible.
+ *
+ * \sa \ref mp4_open_meta().
+ */
+int mp4_open(const struct mp4_callback *cb, struct mp4 **result)
 {
-	return open_file(cb, false, result);
-}
+	struct mp4 *f;
+	int ret;
 
-void mp4_close(struct mp4 *f)
-{
-	int32_t i;
-
-	for (i = 0; i < f->total_tracks; i++) {
-		if (f->track[i]) {
-			free(f->track[i]->stsz_table);
-			free(f->track[i]->stts_sample_count);
-			free(f->track[i]->stsc_first_chunk);
-			free(f->track[i]->stsc_samples_per_chunk);
-			free(f->track[i]->stco_chunk_offset);
-			free(f->track[i]);
-		}
-	}
-	for (i = 0; i < f->meta.count; i++) {
-		free(f->meta.tags[i].item);
-		free(f->meta.tags[i].value);
-	}
-	free(f->meta.tags);
-	free(f);
+	*result = NULL;
+	ret = open_file(cb, false, &f);
+	if (ret < 0)
+		return ret;
+	ret = -E_MP4_BAD_SAMPLE_COUNT;
+	if (f->track.stsz_sample_count == 0)
+		goto fail;
+	ret = -E_MP4_CORRUPT;
+	if (f->track.time_scale == 0)
+		goto fail;
+	*result = f;
+	return 1;
+fail:
+	mp4_close(f);
+	return ret;
 }
 
 static int32_t chunk_of_sample(const struct mp4 *f, int32_t sample,
 		int32_t *chunk)
 {
-	const struct mp4_track *t = f->audio_track;
+	const struct mp4_track *t = &f->track;
 	uint32_t *fc = t->stsc_first_chunk, *spc = t->stsc_samples_per_chunk;
-	int32_t chunk1, chunk1samples, n, total, i;
+	uint32_t chunk1, chunk1samples, n, total, k;
 
-	for (i = 1, total = 0; i < t->stsc_entry_count; i++, total += n) {
-		n = (fc[i] - fc[i - 1]) * spc[i - 1]; /* number of samples */
+	for (k = 1, total = 0; k < t->stsc_entry_count; k++, total += n) {
+		n = (fc[k] - fc[k - 1]) * spc[k - 1]; /* number of samples */
 		if (sample < total + n)
 			break;
 	}
-	chunk1 = fc[i - 1];
-	chunk1samples = spc[i - 1];
+	chunk1 = fc[k - 1];
+	chunk1samples = spc[k - 1];
 	if (chunk1samples != 0)
 		*chunk = (sample - total) / chunk1samples + chunk1;
 	else
@@ -986,22 +706,34 @@ static int32_t chunk_of_sample(const struct mp4 *f, int32_t sample,
 }
 
 /**
- * Return the number of milliseconds of the audio track.
+ * Compute the duration of an mp4 file.
+ *
+ * \param f See \ref mp4_close().
  *
- * \param f As returned by \ref mp4_open_read(), must not be NULL.
+ * \return The number of milliseconds of the audio track. This function never
+ * fails.
  */
 uint64_t mp4_get_duration(const struct mp4 *f)
 {
-	const struct mp4_track *t = f->audio_track;
+	const struct mp4_track *t = &f->track;
 
-	if (t->timeScale == 0)
-		return 0;
-	return t->duration * 1000 / t->timeScale;
+	return t->duration * 1000 / t->time_scale;
 }
 
-int mp4_set_sample_position(struct mp4 *f, int32_t sample)
+/**
+ * Reposition the read/write file offset.
+ *
+ * \param f See \ref mp4_close().
+ * \param sample The number of the sample to reposition to.
+ *
+ * The given sample number must be within range, i.e., strictly less than the
+ * value returned by \ref mp4_num_samples().
+ *
+ * \return Standard. The only possible error is an invalid sample number.
+ */
+int mp4_set_sample_position(struct mp4 *f, uint32_t sample)
 {
-	const struct mp4_track *t = f->audio_track;
+	const struct mp4_track *t = &f->track;
 	int32_t offset, chunk, chunk_sample;
 	uint32_t n, srs; /* sample range size */
 
@@ -1024,36 +756,91 @@ int mp4_set_sample_position(struct mp4 *f, int32_t sample)
 	return 1;
 }
 
-int32_t mp4_get_sample_size(const struct mp4 *f, int sample)
+/**
+ * Look up and return the size of the given sample in the stsz table.
+ *
+ * \param f See \ref mp4_close().
+ * \param sample The sample number of interest.
+ * \param result Sample size is returned here.
+ *
+ * For the sample argument the restriction mentioned in the documentation of
+ * \ref mp4_set_sample_position() applies as well.
+ *
+ * \return Standard. Like for \ref mp4_set_sample_position(), EINVAL is the
+ * only possible error.
+ */
+int mp4_get_sample_size(const struct mp4 *f, uint32_t sample, uint32_t *result)
 {
-	const struct mp4_track *t = f->audio_track;
+	const struct mp4_track *t = &f->track;
 
+	if (sample >= t->stsz_sample_count)
+		return -ERRNO_TO_PARA_ERROR(EINVAL);
 	if (t->stsz_sample_size != 0)
-		return t->stsz_sample_size;
-	return t->stsz_table[sample];
+		*result = t->stsz_sample_size;
+	else
+		*result = t->stsz_table[sample];
+	return 1;
 }
 
-uint32_t mp4_get_sample_rate(const struct mp4 *f)
+/**
+ * Return the sample rate stored in the stsd atom.
+ *
+ * \param f See \ref mp4_close().
+ *
+ * The sample rate is a property of the audio track of the mp4 file and is thus
+ * independent of the sample number.
+ *
+ * \return The function always returns a positive value because the open
+ * operation fails if the sample rate happens to be zero. A typical value is
+ * 44100.
+ */
+uint16_t mp4_get_sample_rate(const struct mp4 *f)
 {
-	return f->audio_track->sampleRate;
+	return f->track.sample_rate;
 }
 
-uint32_t mp4_get_channel_count(const struct mp4 *f)
+/**
+ * Return the number of channels of the audio track.
+ *
+ * \param f See \ref mp4_close().
+ *
+ * \return The returned channel count is guaranteed to be positive because the
+ * open operation fails if the mp4a atom is missing or contains a zero channel
+ * count.
+ */
+uint16_t mp4_get_channel_count(const struct mp4 *f)
 {
-	return f->audio_track->channelCount ;
+	return f->track.channel_count;
 }
 
-int32_t mp4_num_samples(const struct mp4 *f)
+/**
+ * Return the number of samples of the audio track.
+ *
+ * \param f See \ref mp4_close().
+ *
+ * \return The sample count is read from the stsz atom during open.
+ */
+uint32_t mp4_num_samples(const struct mp4 *f)
 {
-	const struct mp4_track *t = f->audio_track;
-	int32_t i;
-	int32_t total = 0;
-
-	for (i = 0; i < t->stts_entry_count; i++)
-		total += t->stts_sample_count[i];
-	return total;
+	return f->track.stsz_sample_count;
 }
 
+/**
+ * Open an mp4 file in metadata-only mode.
+ *
+ * \param cb See \ref mp4_open().
+ * \param result See \ref mp4_open().
+ *
+ * This is similar to \ref mp4_open() but is cheaper because it only parses the
+ * metadata of the mp4 file. The only functions that can subsequently be called
+ * with the file handle returned here are \ref mp4_get_meta() and \ref
+ * mp4_update_meta().
+ *
+ * \return Standard.
+ *
+ * \sa \ref mp4_open(). The comment about ->write() and ->truncate() applies to
+ * this function as well.
+ */
 int mp4_open_meta(const struct mp4_callback *cb, struct mp4 **result)
 {
 	struct mp4 *f;
@@ -1061,11 +848,6 @@ int mp4_open_meta(const struct mp4_callback *cb, struct mp4 **result)
 
 	if (ret < 0)
 		return ret;
-	if (f->udta_size == 0 || f->meta_size == 0 || f->ilst_size == 0) {
-		mp4_close(f);
-		*result = NULL;
-		return -E_MP4_MISSING_ATOM;
-	}
 	*result = f;
 	return 1;
 }
@@ -1073,78 +855,26 @@ int mp4_open_meta(const struct mp4_callback *cb, struct mp4 **result)
 /**
  * Return the metadata of an mp4 file.
  *
- * \param f As returned by either \ref mp4_open_read() or \ref mp4_open_meta().
+ * \param f See \ref mp4_close().
  *
  * The caller is allowed to add, delete or modify the entries of the returned
- * structure in order to pass the modified version to \ref mp4_meta_update().
+ * structure with the intention to pass the modified version to \ref
+ * mp4_update_meta().
+ *
+ * \return This never returns NULL, even if the file contains no metadata tag
+ * items. However, the meta count will be zero and the ->tags pointer NULL in
+ * this case.
  */
 struct mp4_metadata *mp4_get_meta(struct mp4 *f)
 {
 	return &f->meta;
 }
 
-struct membuffer {
-	void *data;
-	unsigned written;
-	unsigned allocated;
-};
-
-static struct membuffer *membuffer_create(void)
-{
-	struct membuffer *buf = para_calloc(sizeof(*buf));
-
-	buf->allocated = 256;
-	buf->data = para_malloc(buf->allocated);
-	return buf;
-}
-
-static void membuffer_write(struct membuffer *buf, const void *ptr,
-		unsigned bytes)
-{
-	unsigned dest_size = buf->written + bytes;
-
-	if (dest_size > buf->allocated) {
-		do {
-			buf->allocated <<= 1;
-		} while (dest_size > buf->allocated);
-		buf->data = para_realloc(buf->data, buf->allocated);
-	}
-
-	if (ptr)
-		memcpy((char *) buf->data + buf->written, ptr, bytes);
-	buf->written += bytes;
-}
-
-static void membuffer_write_atom_name(struct membuffer *buf, const char *data)
+/** Total length of an on-disk metadata tag. */
+#define TAG_LEN(_len) (24 + (_len))
+static void create_ilst(const struct mp4_metadata *meta, uint8_t *out)
 {
-	membuffer_write(buf, data, 4);
-}
-
-static void membuffer_write_int32(struct membuffer *buf, uint32_t data)
-{
-	uint8_t temp[4];
-	write_u32_be(temp, data);
-	membuffer_write(buf, temp, 4);
-}
-
-static unsigned membuffer_get_size(const struct membuffer *buf)
-{
-	return buf->written;
-}
-
-static void *membuffer_detach(struct membuffer *buf)
-{
-	void *ret = para_realloc(buf->data, buf->written);
-	free(buf);
-	return ret;
-}
-
-static void *create_ilst(const struct mp4_metadata *meta, uint32_t *out_size)
-{
-	struct membuffer *buf = membuffer_create();
-	unsigned n;
-
-	for (n = 0; n < meta->count; n++) {
+	for (unsigned n = 0; n < meta->count; n++) {
 		struct mp4_tag *tag = meta->tags + n;
 		unsigned len = strlen(tag->value);
 		const char *atom_name;
@@ -1161,43 +891,35 @@ static void *create_ilst(const struct mp4_metadata *meta, uint32_t *out_size)
 			atom_name = "\xA9" "cmt";
 		else
 			assert(false);
-		membuffer_write_int32(buf, 8 /* atom header */
-			+ 8 /* data atom header */
+		write_u32_be(out, TAG_LEN(len));
+		memcpy(out + 4, atom_name, 4);
+		write_u32_be(out + 8, 8 /* data atom header */
 			+ 8 /* flags + reserved */
 			+ len);
-		membuffer_write_atom_name(buf, atom_name);
-		membuffer_write_int32(buf, 8 /* data atom header */
-			+ 8 /* flags + reserved */
-			+ len);
-		membuffer_write_atom_name(buf, "data");
-		membuffer_write_int32(buf, 1);	/* flags */
-		membuffer_write_int32(buf, 0);	/* reserved */
-		membuffer_write(buf, tag->value, len);
+		memcpy(out + 12, "data", 4);
+		write_u32_be(out + 16, 1); /* flags */
+		write_u32_be(out + 20, 0); /* reserved */
+		memcpy(out + 24, tag->value, len);
+		out += TAG_LEN(len);
 	}
-	*out_size = membuffer_get_size(buf);
-	return membuffer_detach(buf);
-}
-
-static uint32_t fix_byte_order_32(uint32_t src)
-{
-	return read_u32_be(&src);
 }
 
 static void *modify_moov(struct mp4 *f, uint32_t *out_size)
 {
 	int ret;
 	uint64_t total_base = f->moov_offset + 8;
-	uint32_t total_size = (uint32_t) (f->moov_size - 8);
-	uint32_t new_ilst_size;
-	void *new_ilst_buffer, *out_buffer;
+	uint32_t total_size = f->moov_size - 8;
+	uint32_t new_ilst_size = 0;
+	void *out_buffer;
 	uint8_t *p_out;
 	int32_t size_delta;
 	uint32_t tmp;
 
-	new_ilst_buffer = create_ilst(&f->meta, &new_ilst_size);
+	for (unsigned n = 0; n < f->meta.count; n++)
+		new_ilst_size += TAG_LEN(strlen(f->meta.tags[n].value));
 	size_delta = new_ilst_size - (f->ilst_size - 8);
 	*out_size = total_size + size_delta;
-	out_buffer = para_malloc(*out_size);
+	out_buffer = alloc(*out_size);
 	p_out = out_buffer;
 	set_position(f, total_base);
 	ret = read_data(f, p_out, f->udta_offset - total_base);
@@ -1207,7 +929,7 @@ static void *modify_moov(struct mp4 *f, uint32_t *out_size)
 	ret = read_int32(f, &tmp);
 	if (ret <= 0)
 		return NULL;
-	*(uint32_t *)p_out = fix_byte_order_32(tmp + size_delta);
+	write_u32_be(p_out, tmp + size_delta);
 	p_out += 4;
 	ret = read_data(f, p_out, 4);
 	if (ret <= 0)
@@ -1220,7 +942,7 @@ static void *modify_moov(struct mp4 *f, uint32_t *out_size)
 	ret = read_int32(f, &tmp);
 	if (ret <= 0)
 		return NULL;
-	*(uint32_t *)p_out = fix_byte_order_32(tmp + size_delta);
+	write_u32_be(p_out, tmp + size_delta);
 	p_out += 4;
 	ret = read_data(f, p_out, 4);
 	if (ret <= 0)
@@ -1233,45 +955,56 @@ static void *modify_moov(struct mp4 *f, uint32_t *out_size)
 	ret = read_int32(f, &tmp);
 	if (ret <= 0)
 		return NULL;
-	*(uint32_t *)p_out = fix_byte_order_32(tmp + size_delta);
+	write_u32_be(p_out, tmp + size_delta);
 	p_out += 4;
 	ret = read_data(f, p_out, 4);
 	if (ret <= 0)
 		return NULL;
 	p_out += 4;
-	memcpy(p_out, new_ilst_buffer, new_ilst_size);
+	create_ilst(&f->meta, p_out);
 	p_out += new_ilst_size;
 	set_position(f, f->ilst_offset + f->ilst_size);
 	ret = read_data(f, p_out, total_size - (f->ilst_offset - total_base)
 		- f->ilst_size);
 	if (ret <= 0)
 		return NULL;
-	free(new_ilst_buffer);
 	return out_buffer;
 }
 
-static int32_t write_data(struct mp4 *f, void *data, uint32_t size)
+static int write_data(struct mp4 *f, void *data, size_t size)
 {
-	int32_t result = 1;
-
-	result = f->cb->write(f->cb->user_data, data, size);
-
-	f->current_position += size;
-
-	return result;
-}
-
-static int32_t write_int32(struct mp4 *f, uint32_t data)
-{
-	int8_t temp[4];
-	write_u32_be(temp, data);
-	return write_data(f, temp, sizeof(temp));
+	while (size > 0) {
+		ssize_t ret = f->cb->write(f->cb->user_data, data, size);
+		if (ret < 0) {
+			if (errno == EINTR)
+				continue;
+			return -ERRNO_TO_PARA_ERROR(errno);
+		}
+		size -= ret;
+	}
+	return 1;
 }
 
-int32_t mp4_meta_update(struct mp4 *f)
+/**
+ * Write back the modified metadata items to the mp4 file.
+ *
+ * This is the only public function which modifies the contents of an mp4 file.
+ * This is achieved by calling the ->write() and ->truncate() methods of the
+ * callback structure passed to \ref mp4_open() or \ref mp4_open_meta().
+ *
+ * \param f See \ref mp4_close().
+ *
+ * The modified metadata structure does not need to be supplied to this
+ * function because it is part of the mp4 structure.
+ *
+ * \return Standard.
+ */
+int mp4_update_meta(struct mp4 *f)
 {
 	void *new_moov_data;
 	uint32_t new_moov_size;
+	uint8_t buf[8] = "----moov";
+	int ret;
 
 	set_position(f, 0);
 	new_moov_data = modify_moov(f, &new_moov_size);
@@ -1279,93 +1012,45 @@ int32_t mp4_meta_update(struct mp4 *f)
 		mp4_close(f);
 		return 0;
 	}
-	/* copy moov atom to end of the file */
 	if (f->last_atom != ATOM_MOOV) {
-		char *free_data = "free";
-
-		/* rename old moov to free */
 		set_position(f, f->moov_offset + 4);
-		write_data(f, free_data, 4);
-
-		set_position(f, f->file_size);
-		write_int32(f, new_moov_size + 8);
-		write_data(f, "moov", 4);
-		write_data(f, new_moov_data, new_moov_size);
-	} else {
+		ret = write_data(f, "free", 4); /* rename old moov to free */
+		if (ret < 0)
+			goto free_moov;
+		/* write new moov atom at EOF */
+		f->cb->seek(f->cb->user_data, 0, SEEK_END);
+	} else /* overwrite old moov atom */
 		set_position(f, f->moov_offset);
-		write_int32(f, new_moov_size + 8);
-		write_data(f, "moov", 4);
-		write_data(f, new_moov_data, new_moov_size);
-	}
+	write_u32_be(buf, new_moov_size + 8);
+	ret = write_data(f, buf, sizeof(buf));
+	if (ret < 0)
+		goto free_moov;
+	ret = write_data(f, new_moov_data, new_moov_size);
+	if (ret < 0)
+		goto free_moov;
+	ret = f->cb->truncate(f->cb->user_data);
+	if (ret < 0)
+		ret = -ERRNO_TO_PARA_ERROR(errno);
+free_moov:
 	free(new_moov_data);
-	f->cb->truncate(f->cb->user_data);
-	return 1;
-}
-
-static char *meta_find_by_name(const struct mp4 *f, const char *item)
-{
-	uint32_t i;
-
-	for (i = 0; i < f->meta.count; i++)
-		if (!strcasecmp(f->meta.tags[i].item, item))
-			return para_strdup(f->meta.tags[i].value);
-	return NULL;
-}
-
-/**
- * Return the value of the artist meta tag of an mp4 file.
- *
- * \param f Must not be NULL.
- *
- * \return If the file does not contain this metadata tag, the function returns
- * NULL. Otherwise, a copy of the tag value is returned. The caller should free
- * this memory when it is no longer needed.
- */
-char *mp4_meta_get_artist(const struct mp4 *f)
-{
-	return meta_find_by_name(f, "artist");
-}
-
-/**
- * Return the value of the title meta tag of an mp4 file.
- *
- * \param f See \ref mp4_meta_get_artist().
- * \return See \ref mp4_meta_get_artist().
- */
-char *mp4_meta_get_title(const struct mp4 *f)
-{
-	return meta_find_by_name(f, "title");
-}
-
-/**
- * Return the value of the date meta tag of an mp4 file.
- *
- * \param f See \ref mp4_meta_get_artist().
- * \return See \ref mp4_meta_get_artist().
- */
-char *mp4_meta_get_date(const struct mp4 *f)
-{
-	return meta_find_by_name(f, "date");
+	return ret;
 }
 
 /**
- * Return the value of the album meta tag of an mp4 file.
+ * Return the value of the given tag item.
  *
- * \param f See \ref mp4_meta_get_artist().
- * \return See \ref mp4_meta_get_artist().
- */
-char *mp4_meta_get_album(const struct mp4 *f)
-{
-	return meta_find_by_name(f, "album");
-}
-
-/**
- * Return the value of the comment meta tag of an mp4 file.
+ * \param f See \ref mp4_close().
+ * \param item "artist", "title", "album", "comment", or "date".
  *
- * \param f See \ref mp4_meta_get_artist().
- * \return See \ref mp4_meta_get_artist().
+ * \return The function returns NULL if the given item is not in the above
+ * list. Otherwise, if the file does not contain a tag for the given item, the
+ * function also returns NULL. Otherwise a copy of the tag value is returned
+ * and the caller should free this memory when it is no longer needed.
  */
-char *mp4_meta_get_comment(const struct mp4 *f)
+__malloc char *mp4_get_tag_value(const struct mp4 *f, const char *item)
 {
-	return meta_find_by_name(f, "comment");
+	for (unsigned n = 0; n < f->meta.count; n++)
+		if (!strcasecmp(f->meta.tags[n].item, item))
+			return para_strdup(f->meta.tags[n].value);
+	return NULL;
 }