X-Git-Url: http://git.tuebingen.mpg.de/?p=paraslash.git;a=blobdiff_plain;f=mp4.c;h=4b8607b185a9a87c845940d86412843654a13c7d;hp=23bd7934ac87db131331df06e78703d6ec5d0438;hb=HEAD;hpb=153f946f890f7de84d7e2c6e9db6daca2dd3f6ca

diff --git a/mp4.c b/mp4.c
index 23bd7934..fe9d4b37 100644
--- a/mp4.c
+++ b/mp4.c
@@ -5,1975 +5,1052 @@
  * 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"
+#include "error.h"
 #include "portable_io.h"
 #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 {
-	bool is_audio;
-	int32_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 */
-	int32_t stsz_sample_size;
-	int32_t stsz_sample_count;
-	int32_t *stsz_table;
+	uint32_t stsz_sample_size;
+	uint32_t stsz_sample_count;
+	uint32_t *stsz_table;
 
 	/* stts */
-	int32_t stts_entry_count;
-	int32_t *stts_sample_count;
-	int32_t *stts_sample_delta;
+	uint32_t stts_entry_count;
+	uint32_t *stts_sample_count;
 
 	/* stsc */
-	int32_t stsc_entry_count;
-	int32_t *stsc_first_chunk;
-	int32_t *stsc_samples_per_chunk;
-	int32_t *stsc_sample_desc_index;
+	uint32_t stsc_entry_count;
+	uint32_t *stsc_first_chunk;
+	uint32_t *stsc_samples_per_chunk;
 
 	/* stsc */
-	int32_t stco_entry_count;
-	int32_t *stco_chunk_offset;
+	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 {
-	struct mp4_callback *cb;
-	int64_t current_position;
+	const struct mp4_callback *cb;
 
 	uint64_t moov_offset;
 	uint64_t moov_size;
-	uint8_t last_atom;
-	uint64_t file_size;
-
-	uint32_t read_error;
-	uint32_t error;
-
-	/* incremental track index while reading the file */
-	int32_t total_tracks;
-
-	/* track data */
-	struct mp4_track *track[MAX_TRACKS];
+	uint64_t meta_offset;
+	uint32_t meta_size;
+	uint64_t ilst_offset;
+	uint32_t ilst_size;
+	uint64_t udta_offset;
+	uint32_t udta_size;
 
-	/* metadata */
-	struct mp4_metadata tags;
+	uint8_t last_atom;
+	struct mp4_track track;
+	struct mp4_metadata meta;
 };
 
-int32_t mp4_total_tracks(const struct mp4 *f)
-{
-	return f->total_tracks;
-}
-
-static int32_t read_data(struct mp4 *f, void *data, uint32_t size)
+/*
+ * 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)
 {
-	int32_t result = 1;
-
-	result = f->cb->read(f->cb->user_data, data, size);
-
-	if (result < size)
-		f->read_error++;
-
-	f->current_position += size;
-
-	return result;
+	while (size > 0) {
+		ssize_t ret = f->cb->read(f->cb->user_data, data, size);
+		if (ret < 0 && errno == EINTR)
+			continue;
+		/* regard EAGAIN as an error as reads should be blocking. */
+		if (ret <= 0)
+			return ret < 0? -E_MP4_READ : 0;
+		size -= ret;
+	}
+	return 1;
 }
 
-static uint64_t read_int64(struct mp4 *f)
+static int read_int64(struct mp4 *f, uint64_t *result)
 {
 	uint8_t data[8];
+	int ret = read_data(f, data, 8);
 
-	read_data(f, data, 8);
-	return read_u64_be(data);
+	if (ret > 0)
+		*result = read_u64_be(data);
+	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)
+static int read_int32(struct mp4 *f, uint32_t *result)
 {
-	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,
-	ATOM_VMHD = 135,
-	ATOM_SMHD = 136,
-	ATOM_HMHD = 137,
-	ATOM_STSD = 138,
-	ATOM_STTS = 139,
-	ATOM_STSZ = 140,
-	ATOM_STZ2 = 141,
-	ATOM_STCO = 142,
-	ATOM_STSC = 143,
-	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
+	uint8_t data[4];
+	int ret = read_data(f, data, 4);
 
-#define COPYRIGHT_SYMBOL ((int8_t)0xA9)
+	if (ret > 0)
+		*result = read_u32_be(data);
+	return ret;
+}
 
-static uint8_t atom_name_to_type(int8_t a, int8_t b, int8_t c, int8_t d)
+static int read_int16(struct mp4 *f, uint16_t *result)
 {
-	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;
-	}
+	uint8_t data[2];
+	int ret = read_data(f, data, 2);
 
-	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;
+	if (ret > 0)
+		*result = read_u16_be(data);
+	return ret;
 }
 
-/* read atom header, return atom size, atom size is with header included */
-static uint64_t atom_read_header(struct mp4 *f, uint8_t * atom_type,
-				uint8_t * header_size)
-{
-	uint64_t size;
-	int32_t ret;
-	int8_t atom_header[8];
+/** \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)
+{
+	/** 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. */
+static int atom_read_header(struct mp4 *f, uint8_t *atom_type,
+		uint8_t *header_size, uint64_t *atom_size)
+{
+	uint32_t size;
+	int ret;
+	uint8_t atom_header[8];
 
 	ret = read_data(f, atom_header, 8);
-	if (ret != 8)
-		return 0;
-
+	if (ret <= 0)
+		return ret;
 	size = read_u32_be(atom_header);
-	*header_size = 8;
-
-	/* check for 64 bit atom size */
-	if (size == 1) {
-		*header_size = 16;
-		size = read_int64(f);
-	}
-	*atom_type = atom_name_to_type(atom_header[4], atom_header[5],
-		atom_header[6], atom_header[7]);
-	return size;
-}
-
-static int64_t get_position(const struct mp4 *f)
-{
-	return f->current_position;
-}
-
-static int need_parse_when_meta_only(uint8_t atom_type)
-{
-	switch (atom_type) {
-	case ATOM_EDTS:
-	case ATOM_DRMS:
-	case ATOM_SINF:
-	case ATOM_SCHI:
-	case ATOM_STTS:
-	case ATOM_STSZ:
-	case ATOM_STZ2:
-	case ATOM_STCO:
-	case ATOM_STSC:
-	case ATOM_FRMA:
-	case ATOM_IVIV:
-	case ATOM_PRIV:
-		return 0;
-	default:
-		return 1;
+	if (size == 1) { /* 64 bit atom size */
+		if (header_size)
+			*header_size = 16;
+		ret = read_int64(f, atom_size);
+		if (ret <= 0)
+			return ret;
+	} else {
+		if (header_size)
+			*header_size = 8;
+		*atom_size = size;
 	}
+	*atom_type = atom_name_to_type(atom_header + 4);
+	return 1;
 }
 
-static int32_t set_position(struct mp4 *f, int64_t position)
-{
-	f->cb->seek(f->cb->user_data, position);
-	f->current_position = position;
-
-	return 0;
-}
-
-static void track_add(struct mp4 *f)
+static off_t get_position(const struct mp4 *f)
 {
-	f->total_tracks++;
-
-	if (f->total_tracks > MAX_TRACKS) {
-		f->total_tracks = 0;
-		f->error++;
-		return;
-	}
-	f->track[f->total_tracks - 1] = para_calloc(sizeof(struct mp4_track));
+	return f->cb->seek(f->cb->user_data, 0, SEEK_CUR);
 }
 
-static uint8_t read_char(struct mp4 *f)
+static void set_position(struct mp4 *f, off_t position)
 {
-	uint8_t output;
-	read_data(f, &output, 1);
-	return output;
+	f->cb->seek(f->cb->user_data, position, SEEK_SET);
 }
 
-static uint32_t read_int24(struct mp4 *f)
+static void skip_bytes(struct mp4 *f, off_t num_skip)
 {
-	int8_t data[4];
-
-	read_data(f, data, 3);
-	return read_u24_be(data);
+	f->cb->seek(f->cb->user_data, num_skip, SEEK_CUR);
 }
 
-static uint32_t read_int32(struct mp4 *f)
+static int read_stsz(struct mp4 *f)
 {
-	int8_t data[4];
-
-	read_data(f, data, 4);
-	return read_u32_be(data);
-}
+	int ret;
+	struct mp4_track *t = &f->track;
 
-static int32_t read_stsz(struct mp4 *f)
-{
-	int32_t i;
-	struct mp4_track *t;
-
-	if (f->total_tracks == 0)
-		return f->error++;
-	t = f->track[f->total_tracks - 1];
-	read_char(f);	/* version */
-	read_int24(f);	/* flags */
-	t->stsz_sample_size = read_int32(f);
-	t->stsz_sample_count = read_int32(f);
+	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;
+	ret = read_int32(f, &t->stsz_sample_count);
+	if (ret <= 0)
+		return ret;
 	if (t->stsz_sample_size != 0)
-		return 0;
-	t->stsz_table = para_malloc(t->stsz_sample_count * sizeof(int32_t));
-	for (i = 0; i < t->stsz_sample_count && !f->read_error; i++)
-		t->stsz_table[i] = read_int32(f);
-	return 0;
-}
-
-static int32_t read_stts(struct mp4 *f)
-{
-	int32_t i;
-	struct mp4_track *t;
-
-	/* CVE-2017-9223 */
-	if (f->total_tracks == 0)
-		return f->error++;
-	t = f->track[f->total_tracks - 1];
-	if (t->stts_entry_count)
-		return 0;
-	read_char(f);	/* version */
-	read_int24(f);	/* flags */
-	t->stts_entry_count = read_int32(f);
-
-	t->stts_sample_count = para_malloc(t->stts_entry_count
-		* sizeof(int32_t));
-	t->stts_sample_delta = para_malloc(t->stts_entry_count
-		* sizeof (int32_t));
-	/* CVE-2017-9254 */
-	for (i = 0; i < t->stts_entry_count && !f->read_error; i++) {
-		t->stts_sample_count[i] = read_int32(f);
-		t->stts_sample_delta[i] = read_int32(f);
+		return 1;
+	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;
 	}
 	return 1;
 }
 
-static int32_t read_stsc(struct mp4 *f)
+static int read_stts(struct mp4 *f)
 {
-	int32_t i;
-	struct mp4_track *t;
-
-	if (f->total_tracks == 0)
-		return f->error++;
-	t = f->track[f->total_tracks - 1];
-
-	read_char(f);	/* version */
-	read_int24(f);	/* flags */
-	t->stsc_entry_count = read_int32(f);
-	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));
-	t->stsc_sample_desc_index = para_malloc(t->stsc_entry_count *
-		sizeof (int32_t));
+	int ret;
+	struct mp4_track *t = &f->track;
 
-	/* CVE-2017-9255 */
-	for (i = 0; i < t->stsc_entry_count && !f->read_error; i++) {
-		t->stsc_first_chunk[i] = read_int32(f);
-		t->stsc_samples_per_chunk[i] = read_int32(f);
-		t->stsc_sample_desc_index[i] = read_int32(f);
+	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 = 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 0;
-}
-
-static int32_t read_stco(struct mp4 *f)
-{
-	int32_t i;
-	struct mp4_track *t;
-
-	if (f->total_tracks == 0)
-		return f->error++;
-	t = f->track[f->total_tracks - 1];
-
-	read_char(f);	/* version */
-	read_int24(f);	/* flags */
-	t->stco_entry_count = read_int32(f);
-	t->stco_chunk_offset = para_malloc(t->stco_entry_count
-		* sizeof(int32_t));
-	/* CVE-2017-9256 */
-	for (i = 0; i < t->stco_entry_count && !f->read_error; i++)
-		t->stco_chunk_offset[i] = read_int32(f);
-	return 0;
+	return 1;
 }
 
-static uint16_t read_int16(struct mp4 *f)
+static int read_stsc(struct mp4 *f)
 {
-	int8_t data[2];
+	int ret;
+	struct mp4_track *t = &f->track;
 
-	read_data(f, data, 2);
-	return read_u16_be(data);
+	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 = 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[n]);
+		if (ret <= 0)
+			return ret;
+		skip_bytes(f, 4); /* sample desc index */
+	}
+	return 1;
 }
 
-static int32_t read_mp4a(struct mp4 *f)
+static int read_stco(struct mp4 *f)
 {
-	int32_t i;
-	uint8_t atom_type = 0;
-	uint8_t header_size = 0;
-	struct mp4_track *t;
-
-	if (f->total_tracks == 0)
-		return f->error++;
-	t = f->track[f->total_tracks - 1];
+	int ret;
+	struct mp4_track *t = &f->track;
 
-	for (i = 0; i < 6; i++) {
-		read_char(f);	/* reserved */
+	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 = 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;
 	}
-	/* data_reference_index */ read_int16(f);
-
-	read_int32(f);	/* reserved */
-	read_int32(f);	/* reserved */
-
-	t->channelCount = read_int16(f);
-	read_int16(f);
-
-	read_int16(f);
-	read_int16(f);
-
-	t->sampleRate = read_int16(f);
-
-	read_int16(f);
-
-	atom_read_header(f, &atom_type, &header_size);
-	return 0;
+	return 1;
 }
 
-static int32_t read_stsd(struct mp4 *f)
+static int read_stsd(struct mp4 *f)
 {
-	int32_t i, entry_count;
-	uint8_t header_size = 0;
-	struct mp4_track *t;
-
-	/* CVE-2017-9218 */
-	if (f->total_tracks == 0)
-		return f->error++;
-	t = f->track[f->total_tracks - 1];
+	int ret;
+	uint32_t entry_count;
 
-	read_char(f);	/* version */
-	read_int24(f);	/* flags */
-
-	entry_count = read_int32(f);
-
-	/* CVE-2017-9253 */
-	for (i = 0; i < entry_count && !f->read_error; i++) {
+	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 (uint32_t n = 0; n < entry_count; n++) {
 		uint64_t skip = get_position(f);
 		uint64_t size;
 		uint8_t atom_type = 0;
-		size = atom_read_header(f, &atom_type, &header_size);
+		ret = atom_read_header(f, &atom_type, NULL, &size);
+		if (ret <= 0)
+			return ret;
 		skip += size;
-		t->is_audio = atom_type == ATOM_MP4A;
-		if (t->is_audio)
-			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);
 	}
-
-	return 0;
-}
-
-static int32_t tag_add_field(struct mp4_metadata *tags, const char *item,
-		const char *value, int32_t len)
-{
-	if (!item || (item && !*item) || !value)
-		return 0;
-	tags->tags = para_realloc(tags->tags,
-		(tags->count + 1) * sizeof(struct mp4_tag));
-	tags->tags[tags->count].item = para_strdup(item);
-	tags->tags[tags->count].len = len;
-	if (len >= 0) {
-		tags->tags[tags->count].value = para_malloc(len + 1);
-		memcpy(tags->tags[tags->count].value, value, len);
-		tags->tags[tags->count].value[len] = 0;
-	} else {
-		tags->tags[tags->count].value = para_strdup(value);
-	}
-	tags->count++;
 	return 1;
 }
 
-static const char *ID3v1GenreList[] = {
-	"Blues", "Classic Rock", "Country", "Dance", "Disco", "Funk",
-	"Grunge", "Hip-Hop", "Jazz", "Metal", "New Age", "Oldies",
-	"Other", "Pop", "R&B", "Rap", "Reggae", "Rock",
-	"Techno", "Industrial", "Alternative", "Ska", "Death Metal", "Pranks",
-	"Soundtrack", "Euro-Techno", "Ambient", "Trip-Hop", "Vocal",
-	"Jazz+Funk", "Fusion", "Trance", "Classical", "Instrumental", "Acid",
-	"House", "Game", "Sound Clip", "Gospel", "Noise", "AlternRock", "Bass",
-	"Soul", "Punk", "Space", "Meditative", "Instrumental Pop",
-	"Instrumental Rock", "Ethnic", "Gothic", "Darkwave",
-	"Techno-Industrial", "Electronic", "Pop-Folk", "Eurodance", "Dream",
-	"Southern Rock", "Comedy", "Cult", "Gangsta", "Top 40",
-	"Christian Rap", "Pop/Funk", "Jungle", "Native American", "Cabaret",
-	"New Wave", "Psychadelic", "Rave", "Showtunes", "Trailer", "Lo-Fi",
-	"Tribal", "Acid Punk", "Acid Jazz", "Polka", "Retro", "Musical",
-	"Rock & Roll", "Hard Rock", "Folk", "Folk/Rock", "National Folk",
-	"Swing", "Fast-Fusion", "Bebob", "Latin", "Revival", "Celtic",
-	"Bluegrass", "Avantgarde", "Gothic Rock", "Progressive Rock",
-	"Psychedelic Rock", "Symphonic Rock", "Slow Rock", "Big Band",
-	"Chorus", "Easy Listening", "Acoustic", "Humour", "Speech", "Chanson",
-	"Opera", "Chamber Music", "Sonata", "Symphony", "Booty Bass", "Primus",
-	"Porn Groove", "Satire", "Slow Jam", "Club", "Tango", "Samba",
-	"Folklore", "Ballad", "Power Ballad", "Rhythmic Soul", "Freestyle",
-	"Duet", "Punk Rock", "Drum Solo", "A capella", "Euro-House",
-	"Dance Hall", "Goa", "Drum & Bass", "Club House", "Hardcore", "Terror",
-	"Indie", "BritPop", "NegerPunk", "Polsk Punk", "Beat",
-	"Christian Gangsta", "Heavy Metal", "Black Metal", "Crossover",
-	"Contemporary C", "Christian Rock", "Merengue", "Salsa", "Thrash Metal",
-	"Anime", "JPop", "SynthPop",
-};
-
-static const char *meta_index_to_genre(uint32_t idx)
-{
-	if (idx > 0 && idx <= sizeof (ID3v1GenreList) / sizeof (ID3v1GenreList[0])) {
-		return ID3v1GenreList[idx - 1];
-	} else {
-		return 0;
-	}
-}
-
-static char *read_string(struct mp4 *f, uint32_t length)
-{
-	char *str = para_malloc(length + 1);
-	if ((uint32_t)read_data(f, str, length) != length) {
-		free(str);
-		str = NULL;
-	} else
-		str[length] = 0;
-	return str;
-}
-
-static int32_t set_metadata_name(uint8_t atom_type, char **name)
+static const char *get_metadata_name(uint8_t atom_type)
 {
-	static char *tag_names[] = {
-		"unknown", "title", "artist", "writer", "album",
-		"date", "tool", "comment", "genre", "track",
-		"disc", "compilation", "genre", "tempo", "cover",
-		"album_artist", "contentgroup", "lyrics", "description",
-		"network", "show", "episodename",
-		"sorttitle", "sortalbum", "sortartist", "sortalbumartist",
-		"sortwriter", "sortshow",
-		"season", "episode", "podcast"
-	};
-	uint8_t tag_idx = 0;
-
 	switch (atom_type) {
-	case ATOM_TITLE:
-		tag_idx = 1;
-		break;
-	case ATOM_ARTIST:
-		tag_idx = 2;
-		break;
-	case ATOM_WRITER:
-		tag_idx = 3;
-		break;
-	case ATOM_ALBUM:
-		tag_idx = 4;
-		break;
-	case ATOM_DATE:
-		tag_idx = 5;
-		break;
-	case ATOM_TOOL:
-		tag_idx = 6;
-		break;
-	case ATOM_COMMENT:
-		tag_idx = 7;
-		break;
-	case ATOM_GENRE1:
-		tag_idx = 8;
-		break;
-	case ATOM_TRACK:
-		tag_idx = 9;
-		break;
-	case ATOM_DISC:
-		tag_idx = 10;
-		break;
-	case ATOM_COMPILATION:
-		tag_idx = 11;
-		break;
-	case ATOM_GENRE2:
-		tag_idx = 12;
-		break;
-	case ATOM_TEMPO:
-		tag_idx = 13;
-		break;
-	case ATOM_COVER:
-		tag_idx = 14;
-		break;
-	case ATOM_ALBUM_ARTIST:
-		tag_idx = 15;
-		break;
-	case ATOM_CONTENTGROUP:
-		tag_idx = 16;
-		break;
-	case ATOM_LYRICS:
-		tag_idx = 17;
-		break;
-	case ATOM_DESCRIPTION:
-		tag_idx = 18;
-		break;
-	case ATOM_NETWORK:
-		tag_idx = 19;
-		break;
-	case ATOM_SHOW:
-		tag_idx = 20;
-		break;
-	case ATOM_EPISODENAME:
-		tag_idx = 21;
-		break;
-	case ATOM_SORTTITLE:
-		tag_idx = 22;
-		break;
-	case ATOM_SORTALBUM:
-		tag_idx = 23;
-		break;
-	case ATOM_SORTARTIST:
-		tag_idx = 24;
-		break;
-	case ATOM_SORTALBUMARTIST:
-		tag_idx = 25;
-		break;
-	case ATOM_SORTWRITER:
-		tag_idx = 26;
-		break;
-	case ATOM_SORTSHOW:
-		tag_idx = 27;
-		break;
-	case ATOM_SEASON:
-		tag_idx = 28;
-		break;
-	case ATOM_EPISODE:
-		tag_idx = 29;
-		break;
-	case ATOM_PODCAST:
-		tag_idx = 30;
-		break;
-	default:
-		tag_idx = 0;
-		break;
-	}
-
-	*name = para_strdup(tag_names[tag_idx]);
-	return 0;
-}
-
-static uint32_t min_body_size(uint8_t atom_type)
-{
-	switch(atom_type) {
-	case ATOM_GENRE2:
-	case ATOM_TEMPO:
-		return 10;
-	case ATOM_TRACK:
-		return sizeof (char) /* version */
-			+ sizeof(uint8_t) * 3 /* flags */
-			+ sizeof(uint32_t) /* reserved */
-			+ sizeof(uint16_t) /* leading uint16_t */
-			+ sizeof(uint16_t) /* track */
-			+ sizeof(uint16_t); /* totaltracks */
-	case ATOM_DISC:
-		return sizeof (char) /* version */
-			+ sizeof(uint8_t) * 3 /* flags */
-			+ sizeof(uint32_t) /* reserved */
-			+ sizeof(uint16_t) /* disc */
-			+ sizeof(uint16_t); /* totaldiscs */
-	default: assert(false);
+	case ATOM_TITLE: return "title";
+	case ATOM_ARTIST: return "artist";
+	case ATOM_ALBUM: return "album";
+	case ATOM_DATE: return "date";
+	case ATOM_COMMENT: return "comment";
+	default: return "unknown";
 	}
 }
 
-static int32_t parse_tag(struct mp4 *f, uint8_t parent, int32_t size)
+static int parse_tag(struct mp4 *f, uint8_t parent, int32_t size)
 {
-	uint8_t atom_type;
-	uint8_t header_size = 0;
+	int ret;
 	uint64_t subsize, sumsize;
-	char *name = NULL;
-	char *data = NULL;
-	uint32_t done = 0;
+	char *value = NULL;
 	uint32_t len = 0;
 	uint64_t destpos;
+	struct mp4_tag *tag;
 
 	for (
 		sumsize = 0;
-		sumsize < size && !f->read_error; /* CVE-2017-9222 */
+		sumsize < size;
 		set_position(f, destpos), sumsize += subsize
 	) {
-		subsize = atom_read_header(f, &atom_type, &header_size);
+		uint8_t atom_type;
+		uint8_t header_size = 0;
+		ret = atom_read_header(f, &atom_type, &header_size, &subsize);
+		if (ret <= 0)
+			goto fail;
 		destpos = get_position(f) + subsize - header_size;
-		if (done)
-			continue;
-		if (atom_type == ATOM_NAME) {
-			read_char(f);	/* version */
-			read_int24(f);	/* flags */
-			free(name);
-			name = read_string(f, subsize - (header_size + 4));
-			continue;
-		}
 		if (atom_type != ATOM_DATA)
 			continue;
-		read_char(f);	/* version */
-		read_int24(f);	/* flags */
-		read_int32(f);	/* reserved */
-
-		/* some need special attention */
-		if (parent == ATOM_GENRE2 || parent == ATOM_TEMPO) {
-			uint16_t val;
-			if (subsize - header_size < min_body_size(parent))
-				continue;
-			val = read_int16(f);
-			if (parent == ATOM_TEMPO) {
-				char temp[16];
-				sprintf(temp, "%.5u BPM", val);
-				tag_add_field(&(f-> tags), "tempo",
-					temp, -1);
-			} else {
-				const char *tmp = meta_index_to_genre(val);
-				if (tmp)
-					tag_add_field (&(f->tags),
-						"genre", tmp, -1);
-			}
-			done = 1;
-		} else if (parent == ATOM_TRACK || parent == ATOM_DISC) {
-			uint16_t index, total;
-			char temp[32];
-			if (subsize - header_size < min_body_size(parent))
-				continue;
-			read_int16(f);
-			index = read_int16(f);
-			total = read_int16(f);
-			if (parent == ATOM_TRACK)
-				read_int16(f);
-			sprintf(temp, "%d", index);
-			tag_add_field(&(f->tags), parent == ATOM_TRACK?
-				"track" : "disc", temp, -1);
-			if (total > 0) {
-				sprintf(temp, "%d", total);
-				tag_add_field(& (f-> tags),
-					parent == ATOM_TRACK?
-					"totaltracks" : "totaldiscs", temp, -1);
-			}
-			done = 1;
-		} else {
-			free(data);
-			data = read_string(f, subsize - (header_size + 8));
-			len = subsize - (header_size + 8);
-		}
+		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 = alloc(len + 1);
+		ret = read_data(f, value, len);
+		if (ret <= 0)
+			goto fail;
+		value[len] = '\0';
 	}
-	if (data) {
-		if (!done) {
-			if (name == NULL)
-				set_metadata_name(parent , &name);
-			if (name)
-				tag_add_field(&(f->tags), name, data, len);
-		}
-
-		free(data);
-	}
-	free(name);
+	if (!value)
+		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;
+	f->meta.count++;
 	return 1;
+fail:
+	free(value);
+	return ret;
 }
 
-static int32_t read_mdhd(struct mp4 *f)
+static int read_mdhd(struct mp4 *f)
 {
+	int ret;
 	uint32_t version;
-	struct mp4_track *t;
+	struct mp4_track *t = &f->track;
 
-	/* CVE-2017-9221 */
-	if (f->total_tracks == 0)
-		return f->error++;
-	t = f->track[f->total_tracks - 1];
-
-	version = read_int32(f);
+	if (t->state != ATS_INITIAL)
+		return 1;
+	ret = read_int32(f, &version);
+	if (ret <= 0)
+		return ret;
 	if (version == 1) {
-		read_int64(f); //creation-time
-		read_int64(f); //modification-time
-		t->timeScale = read_int32(f); //timescale
-		t->duration = read_int64(f); //duration
-	} else { //version == 0
+		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 */
 		uint32_t temp;
 
-		read_int32(f);	//creation-time
-		read_int32(f);	//modification-time
-		t->timeScale = read_int32(f); //timescale
-		temp = read_int32(f);
+		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);
+		if (ret <= 0)
+			return ret;
 		t->duration = (temp == (uint32_t) (-1))?
 			(uint64_t) (-1) : (uint64_t) (temp);
 	}
-	read_int16(f);
-	read_int16(f);
+	skip_bytes(f, 4);
 	return 1;
 }
 
-static int32_t parse_metadata(struct mp4 *f, int32_t size)
+static int read_ilst(struct mp4 *f, int32_t size)
 {
-	uint64_t subsize, sumsize = 0;
-	uint8_t atom_type;
-	uint8_t header_size = 0;
+	int ret;
+	uint64_t sumsize = 0;
 
 	while (sumsize < size) {
-		subsize = atom_read_header(f, &atom_type, &header_size);
-		if (subsize == 0)
-			break;
-		parse_tag(f, atom_type, (uint32_t)(subsize - header_size));
+		uint8_t atom_type;
+		uint64_t subsize, destpos;
+		uint8_t header_size = 0;
+		ret = atom_read_header(f, &atom_type, &header_size, &subsize);
+		if (ret <= 0)
+			return ret;
+		destpos = get_position(f) + subsize - header_size;
+		switch (atom_type) {
+		case ATOM_ARTIST:
+		case ATOM_TITLE:
+		case ATOM_ALBUM:
+		case ATOM_COMMENT:
+		case ATOM_DATE:
+			ret = parse_tag(f, atom_type, subsize - header_size);
+			if (ret <= 0)
+				return ret;
+		}
+		set_position(f, destpos);
 		sumsize += subsize;
 	}
-
-	return 0;
+	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;
 
-	read_char(f);	/* version */
-	read_int24(f);	/* flags */
-
+	skip_bytes(f, 4); /* version (1), flags (3) */
 	while (sumsize < (size - (header_size + 4))) {
-		subsize = atom_read_header(f, &atom_type, &header_size);
+		ret = atom_read_header(f, &atom_type, &header_size, &subsize);
+		if (ret <= 0)
+			return ret;
 		if (subsize <= header_size + 4)
 			return 1;
 		if (atom_type == ATOM_ILST) {
-			parse_metadata(f, (uint32_t) (subsize - (header_size + 4)));
-		} else {
+			f->ilst_offset = get_position(f) - header_size;
+			f->ilst_size = subsize;
+			ret = read_ilst(f, subsize - (header_size + 4));
+			if (ret <= 0)
+				return ret;
+		} else
 			set_position(f, get_position(f) + subsize - header_size);
-		}
 		sumsize += subsize;
 	}
-
-	return 0;
+	return 1;
 }
 
-static int32_t atom_read(struct mp4 *f, int32_t size, uint8_t atom_type)
+static bool need_atom(uint8_t atom_type, bool meta_only)
 {
-	uint64_t dest_position = get_position(f) + size - 8;
-	if (atom_type == ATOM_STSZ) {
-		/* sample size box */
-		read_stsz(f);
-	} else if (atom_type == ATOM_STTS) {
-		/* time to sample box */
-		read_stts(f);
-	} else if (atom_type == ATOM_STSC) {
-		/* sample to chunk box */
-		read_stsc(f);
-	} else if (atom_type == ATOM_STCO) {
-		/* chunk offset box */
-		read_stco(f);
-	} else if (atom_type == ATOM_STSD) {
-		/* sample description box */
-		read_stsd(f);
-	} else if (atom_type == ATOM_MDHD) {
-		/* track header */
-		read_mdhd(f);
-	} else if (atom_type == ATOM_META) {
-		/* iTunes Metadata box */
-		read_meta(f, size);
+	/* these are needed in any case */
+	switch (atom_type) {
+	case ATOM_STSD:
+	case ATOM_META:
+	case ATOM_TRAK:
+	case ATOM_MDIA:
+	case ATOM_MINF:
+	case ATOM_STBL:
+	case ATOM_UDTA:
+		return true;
 	}
-
-	set_position(f, dest_position);
-	return 0;
+	/* meta-only opens don't need anything else */
+	if (meta_only)
+		return false;
+	/* these are only required for regular opens */
+	switch (atom_type) {
+	case ATOM_STTS:
+	case ATOM_STSZ:
+	case ATOM_STCO:
+	case ATOM_STSC:
+	case ATOM_MDHD:
+		return true;
+	}
+	return false;
 }
 
 /* parse atoms that are sub atoms of other atoms */
-static int32_t parse_sub_atoms(struct mp4 *f, uint64_t total_size, int meta_only)
+static int parse_sub_atoms(struct mp4 *f, uint64_t total_size, bool meta_only)
 {
-	uint64_t size;
-	uint8_t atom_type = 0;
-	uint64_t counted_size = 0;
-	uint8_t header_size = 0;
+	int ret;
+	uint64_t dest, size, end = get_position(f) + total_size;
 
-	while (counted_size < total_size) {
-		size = atom_read_header(f, &atom_type, &header_size);
-		counted_size += size;
-
-		/* check for end of file */
+	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)
-			break;
-
-		/* we're starting to read a new track, update index,
-		 * so that all data and tables get written in the right place
-		 */
-		if (atom_type == ATOM_TRAK)
-			track_add(f);
-		/* parse subatoms */
-		if (meta_only && !need_parse_when_meta_only(atom_type)) {
-			set_position(f, get_position(f) + size - header_size);
-		} else if (atom_type < SUBATOMIC) {
-			parse_sub_atoms(f, size - header_size, meta_only);
-		} else {
-			atom_read(f, (uint32_t) size, atom_type);
+			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;
 		}
-	}
-
-	return 0;
-}
-
-/* parse root atoms */
-static int32_t parse_atoms(struct mp4 *f, int meta_only)
-{
-	uint64_t size;
-	uint8_t atom_type = 0;
-	uint8_t header_size = 0;
-
-	f->file_size = 0;
-	f->read_error = 0;
-
-	while ((size =
-		atom_read_header(f, &atom_type, &header_size)) != 0) {
-		f->file_size += size;
-		f->last_atom = atom_type;
-
-		if (atom_type == ATOM_MOOV && size > header_size) {
-			f->moov_offset = get_position(f) - header_size;
-			f->moov_size = size;
+		if (atom_type == ATOM_UDTA) {
+			f->udta_offset = get_position(f) - header_size;
+			f->udta_size = size;
 		}
-
-		/* parse subatoms */
-		if (meta_only && !need_parse_when_meta_only(atom_type)) {
-			set_position(f, get_position(f) + size - header_size);
-		} else if (atom_type < SUBATOMIC) {
-			parse_sub_atoms(f, size - header_size, meta_only);
-		} else {
-			/* skip this atom */
-			set_position(f, get_position(f) + size - header_size);
+		if (!need_atom(atom_type, meta_only))
+			continue;
+		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);
 		}
+		if (ret <= 0)
+			return ret;
 	}
-
-	return 0;
+	return 1;
 }
 
-struct mp4 *mp4_open_read(struct mp4_callback *cb)
+/**
+ * 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)
 {
-	struct mp4 *f = para_calloc(sizeof(struct mp4));
-
-	f->cb = cb;
-	parse_atoms(f, 0);
-	if (f->error) {
-		free(f);
-		f = NULL;
+	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);
 	}
-	return f;
+	free(f->meta.tags);
+	free(f);
 }
 
-static int32_t tag_delete(struct mp4_metadata *tags)
+static int open_file(const struct mp4_callback *cb, bool meta_only, struct mp4 **result)
 {
-	uint32_t i;
-
-	for (i = 0; i < tags->count; i++) {
-		free(tags->tags[i].item);
-		free(tags->tags[i].value);
-	}
-	free(tags->tags);
-	tags->tags = NULL;
-	tags->count = 0;
-
-	return 0;
-}
+	int ret;
+	uint64_t size;
+	uint8_t atom_type, header_size;
+	struct mp4 *f = zalloc(sizeof(*f));
 
-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]->stts_sample_delta);
-			free(f->track[i]->stsc_first_chunk);
-			free(f->track[i]->stsc_samples_per_chunk);
-			free(f->track[i]->stsc_sample_desc_index);
-			free(f->track[i]->stco_chunk_offset);
-			free(f->track[i]);
+	f->cb = cb;
+	while ((ret = atom_read_header(f, &atom_type, &header_size, &size)) > 0) {
+		f->last_atom = atom_type;
+		if (atom_type != ATOM_MOOV || size <= header_size) { /* skip */
+			set_position(f, get_position(f) + size - header_size);
+			continue;
 		}
+		f->moov_offset = get_position(f) - header_size;
+		f->moov_size = size;
+		ret = parse_sub_atoms(f, size - header_size, meta_only);
+		if (ret <= 0)
+			break;
 	}
+	if (ret < 0)
+		goto fail;
+	ret = -E_MP4_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;
+	mp4_close(f);
+	return ret;
+}
 
-	tag_delete(&(f->tags));
-	free(f);
+/**
+ * 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)
+{
+	struct mp4 *f;
+	int ret;
+
+	*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 track,
-		int32_t sample, int32_t *chunk_sample, int32_t *chunk)
+static int32_t chunk_of_sample(const struct mp4 *f, int32_t sample,
+		int32_t *chunk)
 {
-	int32_t total_entries = 0;
-	int32_t chunk2entry;
-	int32_t chunk1, chunk2, chunk1samples, range_samples, total = 0;
-
-	*chunk_sample = 0;
-	*chunk = 1;
-	if (f->track[track] == NULL) {
-		return -1;
-	}
-
-	total_entries = f->track[track]->stsc_entry_count;
+	const struct mp4_track *t = &f->track;
+	uint32_t *fc = t->stsc_first_chunk, *spc = t->stsc_samples_per_chunk;
+	uint32_t chunk1, chunk1samples, n, total, k;
 
-	chunk1 = 1;
-	chunk1samples = 0;
-	chunk2entry = 0;
-
-	do {
-		chunk2 = f->track[track]->stsc_first_chunk[chunk2entry];
-		*chunk = chunk2 - chunk1;
-		range_samples = *chunk * chunk1samples;
-
-		if (sample < total + range_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;
-
-		chunk1samples = f->track[track]->stsc_samples_per_chunk[chunk2entry];
-		chunk1 = chunk2;
-
-		if (chunk2entry < total_entries) {
-			chunk2entry++;
-			total += range_samples;
-		}
-	} while (chunk2entry < total_entries);
-
-	if (chunk1samples)
+	}
+	chunk1 = fc[k - 1];
+	chunk1samples = spc[k - 1];
+	if (chunk1samples != 0)
 		*chunk = (sample - total) / chunk1samples + chunk1;
 	else
 		*chunk = 1;
-
-	*chunk_sample = total + (*chunk - chunk1) * chunk1samples;
-
-	return 0;
-}
-
-static int32_t chunk_to_offset(const struct mp4 *f, int32_t track,
-		int32_t chunk)
-{
-	const struct mp4_track *p_track = f->track[track];
-
-	if (p_track->stco_entry_count && (chunk > p_track->stco_entry_count)) {
-		return p_track->stco_chunk_offset[p_track->stco_entry_count -
-						  1];
-	} else if (p_track->stco_entry_count) {
-		return p_track->stco_chunk_offset[chunk - 1];
-	} else {
-		return 8;
-	}
-
-	return 0;
-}
-
-static int32_t sample_range_size(const struct mp4 *f, int32_t track,
-		int32_t chunk_sample, int32_t sample)
-{
-	int32_t i, total;
-	const struct mp4_track *p_track = f->track[track];
-
-	if (p_track->stsz_sample_size) {
-		return (sample - chunk_sample) * p_track->stsz_sample_size;
-	} else {
-		if (sample >= p_track->stsz_sample_count)
-			return 0;	//error
-
-		for (i = chunk_sample, total = 0; i < sample; i++) {
-			total += p_track->stsz_table[i];
-		}
-	}
-
-	return total;
-}
-
-static int32_t sample_to_offset(const struct mp4 *f, int32_t track,
-		int32_t sample)
-{
-	int32_t chunk, chunk_sample, chunk_offset1, chunk_offset2;
-
-	chunk_of_sample(f, track, sample, &chunk_sample, &chunk);
-
-	chunk_offset1 = chunk_to_offset(f, track, chunk);
-	chunk_offset2 = chunk_offset1 + sample_range_size(f,
-		track, chunk_sample, sample);
-	return chunk_offset2;
+	return total + (*chunk - chunk1) * chunk1samples;
 }
 
 /**
- * Return the number of milliseconds of the given track.
+ * Compute the duration of an mp4 file.
  *
- * \param f As returned by \ref mp4_open_read(), must not be NULL.
- * \param track Between zero and the value returned by \ref mp4_total_tracks().
+ * \param f See \ref mp4_close().
  *
- * The function returns zero if the audio file is of zero length or contains a
- * corrupt track header.
+ * \return The number of milliseconds of the audio track. This function never
+ * fails.
  */
-uint64_t mp4_get_duration(const struct mp4 *f, int32_t track)
+uint64_t mp4_get_duration(const struct mp4 *f)
 {
-	const struct mp4_track *t = f->track[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;
 }
 
 /**
- * Check whether the given track number corresponds to an audio track.
+ * Reposition the read/write file offset.
+ *
+ * \param f See \ref mp4_close().
+ * \param sample The number of the sample to reposition to.
  *
- * \param f See \ref mp4_get_duration().
- * \param track See \ref mp4_get_duration().
+ * The given sample number must be within range, i.e., strictly less than the
+ * value returned by \ref mp4_num_samples().
  *
- * Besides audio tracks, an mp4 file may contain video and system tracks. For
- * those the function returns false.
+ * \return Standard. The only possible error is an invalid sample number.
  */
-bool mp4_is_audio_track(const struct mp4 *f, int32_t track)
-{
-	return f->track[track]->is_audio;
-}
-
-void mp4_set_sample_position(struct mp4 *f, int32_t track, int32_t sample)
-{
-	int32_t offset = sample_to_offset(f, track, sample);
-	set_position(f, offset);
-}
-
-int32_t mp4_get_sample_size(const struct mp4 *f, int track, int sample)
-{
-	const struct mp4_track *t = f->track[track];
-
-	if (t->stsz_sample_size != 0)
-		return t->stsz_sample_size;
-	return t->stsz_table[sample];
-}
-
-uint32_t mp4_get_sample_rate(const struct mp4 *f, int32_t track)
-{
-	return f->track[track]->sampleRate;
-}
-
-uint32_t mp4_get_channel_count(const struct mp4 *f, int32_t track)
-{
-	return f->track[track]->channelCount;
-}
-
-int32_t mp4_num_samples(const struct mp4 *f, int32_t track)
-{
-	int32_t i;
-	int32_t total = 0;
-
-	for (i = 0; i < f->track[track]->stts_entry_count; i++) {
-		total += f->track[track]->stts_sample_count[i];
-	}
-	return total;
-}
-
-struct mp4 *mp4_open_meta(struct mp4_callback *cb)
-{
-	struct mp4 *f = para_calloc(sizeof(struct mp4));
-
-	f->cb = cb;
-	parse_atoms(f, 1);
-	if (f->error) {
-		free(f);
-		f = NULL;
-	}
-	return f;
-}
-
-int32_t mp4_meta_get_num_items(const struct mp4 *f)
-{
-	return f->tags.count;
-}
-
-int32_t mp4_meta_get_by_index(const struct mp4 *f, uint32_t index,
-				char **item, char **value)
-{
-	if (index >= f->tags.count) {
-		*item = NULL;
-		*value = NULL;
-		return 0;
-	} else {
-		*item = para_strdup(f->tags.tags[index].item);
-		*value = para_strdup(f->tags.tags[index].value);
-		return 1;
-	}
-}
-
-static uint32_t find_atom(struct mp4 *f, uint64_t base, uint32_t size,
-			  const char *name)
-{
-	uint32_t remaining = size;
-	uint64_t atom_offset = base;
-	for (;;) {
-		char atom_name[4];
-		uint32_t atom_size;
-
-		set_position(f, atom_offset);
-
-		if (remaining < 8)
-			break;
-		atom_size = read_int32(f);
-		if (atom_size > remaining || atom_size < 8)
-			break;
-		read_data(f, atom_name, 4);
-
-		if (!memcmp(atom_name, name, 4)) {
-			set_position(f, atom_offset);
-			return 1;
-		}
-
-		remaining -= atom_size;
-		atom_offset += atom_size;
-	}
-	return 0;
-}
-
-static uint32_t find_atom_v2(struct mp4 *f, uint64_t base, uint32_t size,
-		const char *name, uint32_t extraheaders, const char *name_inside)
-{
-	uint64_t first_base = (uint64_t) (-1);
-	while (find_atom(f, base, size, name))	//try to find atom <name> with atom <name_inside> in it
-	{
-		uint64_t mybase = get_position(f);
-		uint32_t mysize = read_int32(f);
-
-		if (first_base == (uint64_t) (-1))
-			first_base = mybase;
-
-		if (mysize < 8 + extraheaders)
-			break;
-
-		if (find_atom (f, mybase + (8 + extraheaders),
-				mysize - (8 + extraheaders), name_inside)) {
-			set_position(f, mybase);
-			return 2;
-		}
-		base += mysize;
-		if (size <= mysize) {
-			size = 0;
-			break;
-		}
-		size -= mysize;
-	}
-
-	if (first_base != (uint64_t) (-1))	//wanted atom inside not found
-	{
-		set_position(f, first_base);
-		return 1;
-	} else
-		return 0;
-}
-
-struct membuffer {
-	void *data;
-	unsigned written;
-	unsigned allocated;
-	unsigned error;
-};
-
-static struct membuffer *membuffer_create(void)
-{
-	const unsigned initial_size = 256;
-
-	struct membuffer *buf = para_malloc(sizeof(*buf));
-	buf->data = para_malloc(initial_size);
-	buf->written = 0;
-	buf->allocated = initial_size;
-	buf->error = buf->data == 0 ? 1 : 0;
-
-	return buf;
-}
-
-static unsigned membuffer_write(struct membuffer *buf, const void *ptr, unsigned bytes)
-{
-	unsigned dest_size = buf->written + bytes;
-
-	if (buf->error)
-		return 0;
-	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;
-	return bytes;
-}
-
-static unsigned membuffer_write_atom_name(struct membuffer *buf, const char *data)
-{
-	return membuffer_write(buf, data, 4) == 4 ? 1 : 0;
-}
-
-static unsigned membuffer_write_int16(struct membuffer *buf, uint16_t data)
-{
-	uint8_t temp[2];
-
-	write_u16_be(temp, data);
-	return membuffer_write(buf, temp, 2);
-}
-
-static unsigned membuffer_write_int32(struct membuffer *buf, uint32_t data)
-{
-	uint8_t temp[4];
-	write_u32_be(temp, data);
-	return membuffer_write(buf, temp, 4);
-}
-
-static void membuffer_write_track_tag(struct membuffer *buf, const char *name,
-		uint32_t index, uint32_t total)
-{
-	membuffer_write_int32(buf,
-		8 /*atom header */  + 8 /*data atom header */  +
-		8 /*flags + reserved */  + 8 /*actual data */ );
-	membuffer_write_atom_name(buf, name);
-	membuffer_write_int32(buf,
-		8 /*data atom header */  +
-		8 /*flags + reserved */  + 8 /*actual data */ );
-	membuffer_write_atom_name(buf, "data");
-	membuffer_write_int32(buf, 0);	//flags
-	membuffer_write_int32(buf, 0);	//reserved
-	membuffer_write_int16(buf, 0);
-	membuffer_write_int16(buf, (uint16_t) index);	//track number
-	membuffer_write_int16(buf, (uint16_t) total);	//total tracks
-	membuffer_write_int16(buf, 0);
-}
-
-static void membuffer_write_int16_tag(struct membuffer *buf, const char *name,
-		uint16_t value)
-{
-	membuffer_write_int32(buf,
-		8 /*atom header */  + 8 /*data atom header */  +
-		8 /*flags + reserved */  + 2 /*actual data */ );
-	membuffer_write_atom_name(buf, name);
-	membuffer_write_int32(buf,
-		8 /*data atom header */  +
-		8 /*flags + reserved */  + 2 /*actual data */ );
-	membuffer_write_atom_name(buf, "data");
-	membuffer_write_int32(buf, 0);	//flags
-	membuffer_write_int32(buf, 0);	//reserved
-	membuffer_write_int16(buf, value);	//value
-}
-
-static uint32_t myatoi(const char *param)
-{
-	return param ? atoi(param) : 0;
-}
-
-static uint32_t meta_genre_to_index(const char *genrestr)
-{
-	unsigned n;
-	for (n = 0; n < sizeof (ID3v1GenreList) / sizeof (ID3v1GenreList[0]); n++) {
-		if (!strcasecmp(genrestr, ID3v1GenreList[n]))
-			return n + 1;
+int mp4_set_sample_position(struct mp4 *f, uint32_t sample)
+{
+	const struct mp4_track *t = &f->track;
+	int32_t offset, chunk, chunk_sample;
+	uint32_t n, srs; /* sample range size */
+
+	if (sample >= t->stsz_sample_count)
+		return -ERRNO_TO_PARA_ERROR(EINVAL);
+	chunk_sample = chunk_of_sample(f, sample, &chunk);
+	if (t->stsz_sample_size > 0)
+		srs = (sample - chunk_sample) * t->stsz_sample_size;
+	else {
+		for (srs = 0, n = chunk_sample; n < sample; n++)
+			srs += t->stsz_table[n];
 	}
-	return 0;
-}
-
-struct stdmeta_entry {
-	const char *atom;
-	const char *name;
-};
-
-struct stdmeta_entry stdmetas[] = {
-	{"\xA9" "nam", "title"},
-	{"\xA9" "ART", "artist"},
-	{"\xA9" "wrt", "writer"},
-	{"\xA9" "alb", "album"},
-	{"\xA9" "day", "date"},
-	{"\xA9" "too", "tool"},
-	{"\xA9" "cmt", "comment"},
-	{"cpil", "compilation"},
-	{"covr", "cover"},
-	{"aART", "album_artist"},
-};
-
-static const char *find_standard_meta(const char *name)	//returns atom name if found, 0 if not
-{
-	unsigned n;
-	for (n = 0; n < sizeof (stdmetas) / sizeof (stdmetas[0]); n++) {
-		if (!strcasecmp(name, stdmetas[n].name))
-			return stdmetas[n].atom;
-	}
-	return 0;
-}
-
-static void membuffer_write_std_tag(struct membuffer *buf, const char *name,
-		const char *value)
-{
-	uint32_t flags = 1;
-
-	/* special check for compilation flag */
-	if (strcmp(name, "cpil") == 0) {
-		flags = 21;
-	}
-
-	membuffer_write_int32(buf,
-		8 /*atom header */  + 8 /*data atom header */  +
-		8 /*flags + reserved */  + strlen(value));
-	membuffer_write_atom_name(buf, name);
-	membuffer_write_int32(buf,
-		8 /*data atom header */  +
-		8 /*flags + reserved */  + strlen(value));
-	membuffer_write_atom_name(buf, "data");
-	membuffer_write_int32(buf, flags);	//flags
-	membuffer_write_int32(buf, 0);	//reserved
-	membuffer_write(buf, value, strlen(value));
-}
-
-static void membuffer_write_custom_tag(struct membuffer *buf, const char *name,
-		const char *value)
-{
-	membuffer_write_int32(buf,
-		8 /*atom header */  +
-		0x1C /*weirdo itunes atom */  +
-		12 /*name atom header */  + strlen(name) +
-		16 /*data atom header + flags */  + strlen(value));
-	membuffer_write_atom_name(buf, "----");
-	membuffer_write_int32(buf, 0x1C);	//weirdo itunes atom
-	membuffer_write_atom_name(buf, "mean");
-	membuffer_write_int32(buf, 0);
-	membuffer_write(buf, "com.apple.iTunes", 16);
-	membuffer_write_int32(buf, 12 + strlen(name));
-	membuffer_write_atom_name(buf, "name");
-	membuffer_write_int32(buf, 0);
-	membuffer_write(buf, name, strlen(name));
-	membuffer_write_int32(buf,
-		8 /*data atom header */  +
-		8 /*flags + reserved */  + strlen(value));
-	membuffer_write_atom_name(buf, "data");
-	membuffer_write_int32(buf, 1);	//flags
-	membuffer_write_int32(buf, 0);	//reserved
-	membuffer_write(buf, value, strlen(value));
-}
-
-static unsigned membuffer_error(const struct membuffer *buf)
-{
-	return buf->error;
-}
-
-static void membuffer_free(struct membuffer *buf)
-{
-	free(buf->data);
-	free(buf);
-}
-
-static unsigned membuffer_get_size(const struct membuffer *buf)
-{
-	return buf->written;
-}
-
-static void *membuffer_detach(struct membuffer *buf)
-{
-	void *ret;
-
-	if (buf->error)
-		return 0;
-	ret = para_realloc(buf->data, buf->written);
-	buf->data = 0;
-	buf->error = 1;
-	return ret;
-}
-
-static uint32_t create_ilst(const struct mp4_metadata *data, void **out_buffer,
-		uint32_t * out_size)
-{
-	struct membuffer *buf = membuffer_create();
-	unsigned metaptr;
-	char *mask = para_calloc(data->count);
-	const char *tracknumber_ptr = 0, *totaltracks_ptr = 0;
-	const char *discnumber_ptr = 0, *totaldiscs_ptr = 0;
-	const char *genre_ptr = 0, *tempo_ptr = 0;
-
-	for (metaptr = 0; metaptr < data->count; metaptr++) {
-		struct mp4_tag *tag = &data->tags[metaptr];
-		if (!strcasecmp(tag->item, "tracknumber")
-				|| !strcasecmp(tag->item, "track")) {
-			if (tracknumber_ptr == 0)
-				tracknumber_ptr = tag->value;
-			mask[metaptr] = 1;
-		} else if (!strcasecmp(tag->item, "totaltracks")) {
-			if (totaltracks_ptr == 0)
-				totaltracks_ptr = tag->value;
-			mask[metaptr] = 1;
-		} else if (!strcasecmp(tag->item, "discnumber")
-				|| !strcasecmp(tag->item, "disc")) {
-			if (discnumber_ptr == 0)
-				discnumber_ptr = tag->value;
-			mask[metaptr] = 1;
-		} else if (!strcasecmp(tag->item, "totaldiscs")) {
-			if (totaldiscs_ptr == 0)
-				totaldiscs_ptr = tag->value;
-			mask[metaptr] = 1;
-		} else if (!strcasecmp(tag->item, "genre")) {
-			if (genre_ptr == 0)
-				genre_ptr = tag->value;
-			mask[metaptr] = 1;
-		} else if (!strcasecmp(tag->item, "tempo")) {
-			if (tempo_ptr == 0)
-				tempo_ptr = tag->value;
-			mask[metaptr] = 1;
-		}
-	}
-
-	if (tracknumber_ptr)
-		membuffer_write_track_tag(buf, "trkn", myatoi(tracknumber_ptr),
-			 myatoi(totaltracks_ptr));
-	if (discnumber_ptr)
-		membuffer_write_track_tag(buf, "disk", myatoi(discnumber_ptr),
-			 myatoi(totaldiscs_ptr));
-	if (tempo_ptr)
-		membuffer_write_int16_tag(buf, "tmpo", myatoi(tempo_ptr));
-
-	if (genre_ptr) {
-		uint32_t index = meta_genre_to_index(genre_ptr);
-		if (index == 0)
-			membuffer_write_std_tag(buf, "©gen", genre_ptr);
-		else
-			membuffer_write_int16_tag(buf, "gnre", index);
-	}
-	for (metaptr = 0; metaptr < data->count; metaptr++) {
-		struct mp4_tag *tag;
-		const char *std_meta_atom;
-
-		if (mask[metaptr])
-			continue;
-		tag = &data->tags[metaptr];
-		std_meta_atom = find_standard_meta(tag->item);
-		if (std_meta_atom)
-			membuffer_write_std_tag(buf, std_meta_atom, tag->value);
-		else
-			membuffer_write_custom_tag(buf, tag->item, tag->value);
-	}
-	free(mask);
-
-	if (membuffer_error(buf)) {
-		membuffer_free(buf);
-		return 0;
-	}
-
-	*out_size = membuffer_get_size(buf);
-	*out_buffer = membuffer_detach(buf);
-	membuffer_free(buf);
-
+	if (t->stco_entry_count > 0 && chunk > t->stco_entry_count)
+		offset = t->stco_chunk_offset[t->stco_entry_count - 1];
+	else if (t->stco_entry_count > 0)
+		offset = t->stco_chunk_offset[chunk - 1];
+	else
+		offset = 8;
+	set_position(f, offset + srs);
 	return 1;
 }
 
-static void membuffer_write_atom(struct membuffer *buf, const char *name, unsigned size,
-			  const void *data)
+/**
+ * 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)
 {
-	membuffer_write_int32(buf, size + 8);
-	membuffer_write_atom_name(buf, name);
-	membuffer_write(buf, data, size);
-}
+	const struct mp4_track *t = &f->track;
 
-static void *membuffer_get_ptr(const struct membuffer *buf)
-{
-	return buf->data;
+	if (sample >= t->stsz_sample_count)
+		return -ERRNO_TO_PARA_ERROR(EINVAL);
+	if (t->stsz_sample_size != 0)
+		*result = t->stsz_sample_size;
+	else
+		*result = t->stsz_table[sample];
+	return 1;
 }
 
-static void membuffer_set_error(struct membuffer *buf)
+/**
+ * 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)
 {
-	buf->error = 1;
+	return f->track.sample_rate;
 }
 
-static unsigned membuffer_transfer_from_file(struct membuffer *buf, struct mp4 *src,
-		unsigned bytes)
+/**
+ * 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)
 {
-	unsigned oldsize;
-	void *bufptr;
-
-	oldsize = membuffer_get_size(buf);
-	if (membuffer_write(buf, 0, bytes) != bytes)
-		return 0;
-
-	bufptr = membuffer_get_ptr(buf);
-	if (bufptr == 0)
-		return 0;
-
-	if ((unsigned)read_data(src, (char *) bufptr + oldsize, bytes) !=
-		bytes) {
-		membuffer_set_error(buf);
-		return 0;
-	}
-
-	return bytes;
+	return f->track.channel_count;
 }
 
-static uint32_t create_meta(const struct mp4_metadata *data, void **out_buffer,
-		uint32_t * out_size)
+/**
+ * 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)
 {
-	struct membuffer *buf;
-	uint32_t ilst_size;
-	void *ilst_buffer;
-
-	if (!create_ilst(data, &ilst_buffer, &ilst_size))
-		return 0;
-
-	buf = membuffer_create();
-
-	membuffer_write_int32(buf, 0);
-	membuffer_write_atom(buf, "ilst", ilst_size, ilst_buffer);
-	free(ilst_buffer);
-
-	*out_size = membuffer_get_size(buf);
-	*out_buffer = membuffer_detach(buf);
-	membuffer_free(buf);
-	return 1;
+	return f->track.stsz_sample_count;
 }
 
-static uint32_t create_udta(const struct mp4_metadata *data, void **out_buffer,
-uint32_t * out_size)
+/**
+ * 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 membuffer *buf;
-	uint32_t meta_size;
-	void *meta_buffer;
+	struct mp4 *f;
+	int ret = open_file(cb, true, &f);
 
-	if (!create_meta(data, &meta_buffer, &meta_size))
-		return 0;
-
-	buf = membuffer_create();
-
-	membuffer_write_atom(buf, "meta", meta_size, meta_buffer);
-
-	free(meta_buffer);
-
-	*out_size = membuffer_get_size(buf);
-	*out_buffer = membuffer_detach(buf);
-	membuffer_free(buf);
+	if (ret < 0)
+		return ret;
+	*result = f;
 	return 1;
 }
 
-static uint32_t fix_byte_order_32(uint32_t src)
-{
-	return read_u32_be(&src);
+/**
+ * Return the metadata of an mp4 file.
+ *
+ * \param f See \ref mp4_close().
+ *
+ * The caller is allowed to add, delete or modify the entries of the returned
+ * 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;
+}
+
+/** 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)
+{
+	for (unsigned n = 0; n < meta->count; n++) {
+		struct mp4_tag *tag = meta->tags + n;
+		unsigned len = strlen(tag->value);
+		const char *atom_name;
+
+		if (!strcasecmp(tag->item, "title"))
+			atom_name = "\xA9" "nam";
+		else if (!strcasecmp(tag->item, "artist"))
+			atom_name = "\xA9" "ART";
+		else if (!strcasecmp(tag->item, "album"))
+			atom_name = "\xA9" "alb";
+		else if (!strcasecmp(tag->item, "date"))
+			atom_name = "\xA9" "day";
+		else if (!strcasecmp(tag->item, "comment"))
+			atom_name = "\xA9" "cmt";
+		else
+			assert(false);
+		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);
+		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);
+	}
 }
 
-static uint32_t modify_moov(struct mp4 *f, const struct mp4_metadata *data,
-		void **out_buffer, uint32_t * out_size)
+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);
-
-	uint64_t udta_offset, meta_offset, ilst_offset;
-	uint32_t udta_size, meta_size, ilst_size;
-
-	uint32_t new_ilst_size;
-	void *new_ilst_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;
-
-	if (!find_atom_v2(f, total_base, total_size, "udta", 0, "meta")) {
-		struct membuffer *buf;
-		void *new_udta_buffer;
-		uint32_t new_udta_size;
-		if (!create_udta(data, &new_udta_buffer, &new_udta_size))
-			return 0;
-
-		buf = membuffer_create();
-		set_position(f, total_base);
-		membuffer_transfer_from_file(buf, f, total_size);
-
-		membuffer_write_atom(buf, "udta", new_udta_size,
-			new_udta_buffer);
-
-		free(new_udta_buffer);
-
-		*out_size = membuffer_get_size(buf);
-		*out_buffer = membuffer_detach(buf);
-		membuffer_free(buf);
-		return 1;
-	} else {
-		udta_offset = get_position(f);
-		udta_size = read_int32(f);
-		if (!find_atom_v2 (f, udta_offset + 8, udta_size - 8, "meta", 4, "ilst")) {
-			struct membuffer *buf;
-			void *new_meta_buffer;
-			uint32_t new_meta_size;
-			if (!create_meta(data, &new_meta_buffer, &new_meta_size))
-				return 0;
-
-			buf = membuffer_create();
-			set_position(f, total_base);
-			membuffer_transfer_from_file(buf, f,
-				(uint32_t)(udta_offset - total_base));
-
-			membuffer_write_int32(buf, udta_size + 8 + new_meta_size);
-			membuffer_write_atom_name(buf, "udta");
-			membuffer_transfer_from_file(buf, f, udta_size);
-
-			membuffer_write_atom(buf, "meta", new_meta_size,
-				new_meta_buffer);
-			free(new_meta_buffer);
-
-			*out_size = membuffer_get_size(buf);
-			*out_buffer = membuffer_detach(buf);
-			membuffer_free(buf);
-			return 1;
+	uint32_t tmp;
+
+	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 = alloc(*out_size);
+	p_out = out_buffer;
+	set_position(f, total_base);
+	ret = read_data(f, p_out, f->udta_offset - total_base);
+	if (ret <= 0)
+		return NULL;
+	p_out += f->udta_offset - total_base;
+	ret = read_int32(f, &tmp);
+	if (ret <= 0)
+		return NULL;
+	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;
+	ret = read_data(f, p_out, f->meta_offset - f->udta_offset - 8);
+	if (ret <= 0)
+		return NULL;
+	p_out += f->meta_offset - f->udta_offset - 8;
+	ret = read_int32(f, &tmp);
+	if (ret <= 0)
+		return NULL;
+	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;
+	ret = read_data(f, p_out, f->ilst_offset - f->meta_offset - 8);
+	if (ret <= 0)
+		return NULL;
+	p_out += f->ilst_offset - f->meta_offset - 8;
+	ret = read_int32(f, &tmp);
+	if (ret <= 0)
+		return NULL;
+	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;
+	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;
+	return out_buffer;
+}
+
+static int write_data(struct mp4 *f, void *data, size_t size)
+{
+	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);
 		}
-		meta_offset = get_position(f);
-		meta_size = read_int32(f);
-		if (!find_atom(f, meta_offset + 12, meta_size - 12, "ilst"))
-			return 0;	//shouldn't happen, find_atom_v2 above takes care of it
-		ilst_offset = get_position(f);
-		ilst_size = read_int32(f);
-
-		if (!create_ilst(data, &new_ilst_buffer, &new_ilst_size))
-			return 0;
-
-		size_delta = new_ilst_size - (ilst_size - 8);
-
-		*out_size = total_size + size_delta;
-		*out_buffer = para_malloc(*out_size);
-		p_out = (uint8_t *) * out_buffer;
-
-		set_position(f, total_base);
-		read_data(f, p_out,
-				(uint32_t) (udta_offset - total_base));
-		p_out += (uint32_t) (udta_offset - total_base);
-		*(uint32_t *) p_out = fix_byte_order_32(read_int32(f) + size_delta);
-		p_out += 4;
-		read_data(f, p_out, 4);
-		p_out += 4;
-		read_data(f, p_out,
-				(uint32_t) (meta_offset - udta_offset - 8));
-		p_out += (uint32_t) (meta_offset - udta_offset - 8);
-		*(uint32_t *) p_out = fix_byte_order_32(read_int32(f) + size_delta);
-		p_out += 4;
-		read_data(f, p_out, 4);
-		p_out += 4;
-		read_data(f, p_out,
-				(uint32_t) (ilst_offset - meta_offset - 8));
-		p_out += (uint32_t) (ilst_offset - meta_offset - 8);
-		*(uint32_t *) p_out = fix_byte_order_32(read_int32(f) + size_delta);
-		p_out += 4;
-		read_data(f, p_out, 4);
-		p_out += 4;
-
-		memcpy(p_out, new_ilst_buffer, new_ilst_size);
-		p_out += new_ilst_size;
-
-		set_position(f, ilst_offset + ilst_size);
-		read_data(f, p_out, (uint32_t) (total_size
-			- (ilst_offset - total_base) - ilst_size));
-
-		free(new_ilst_buffer);
+		size -= ret;
 	}
 	return 1;
 }
 
-static int32_t write_data(struct mp4 *f, void *data, uint32_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));
-}
-
-int32_t mp4_meta_update(struct mp4_callback *cb, const struct mp4_metadata *data)
+/**
+ * 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;
 
-	struct mp4 *f = para_calloc(sizeof(struct mp4));
-	f->cb = cb;
 	set_position(f, 0);
-	parse_atoms(f, 1);
-	if (!modify_moov(f, data, &new_moov_data, &new_moov_size)) {
+	new_moov_data = modify_moov(f, &new_moov_size);
+	if (!new_moov_data ) {
 		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);
-	}
-	cb->truncate(cb->user_data);
-	mp4_close(f);
-	return 1;
-}
-
-/* find a metadata item by name */
-/* returns 0 if item found, 1 if no such item */
-static int32_t meta_find_by_name(const struct mp4 *f, const char *item,
-		char **value)
-{
-	uint32_t i;
-
-	for (i = 0; i < f->tags.count; i++) {
-		if (!strcasecmp(f->tags.tags[i].item, item)) {
-			*value = para_strdup(f->tags.tags[i].value);
-			return 1;
-		}
-	}
-
-	*value = NULL;
-
-	/* not found */
-	return 0;
-}
-
-int32_t mp4_meta_get_artist(const struct mp4 *f, char **value)
-{
-	return meta_find_by_name(f, "artist", value);
-}
-
-int32_t mp4_meta_get_title(const struct mp4 *f, char **value)
-{
-	return meta_find_by_name(f, "title", value);
-}
-
-int32_t mp4_meta_get_date(const struct mp4 *f, char **value)
-{
-	return meta_find_by_name(f, "date", value);
-}
-
-int32_t mp4_meta_get_album(const struct mp4 *f, char **value)
-{
-	return meta_find_by_name(f, "album", value);
+	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);
+	return ret;
 }
 
-int32_t mp4_meta_get_comment(const struct mp4 *f, char **value)
+/**
+ * Return the value of the given tag item.
+ *
+ * \param f See \ref mp4_close().
+ * \param item "artist", "title", "album", "comment", or "date".
+ *
+ * \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.
+ */
+__malloc char *mp4_get_tag_value(const struct mp4 *f, const char *item)
 {
-	return meta_find_by_name(f, "comment", value);
+	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;
 }