X-Git-Url: http://git.tuebingen.mpg.de/?a=blobdiff_plain;f=mp4.c;h=7145a47a829695e2cf82a46f58b18aa743c30246;hb=b96d1f30be6fda4b3d93aef19e66273260503cac;hp=535c785aa1c62443697d8f0c78fabb29759270c0;hpb=89a8a29712c0d36f69646ace62fd02abe2ce0672;p=paraslash.git

diff --git a/mp4.c b/mp4.c
index 535c785a..7145a47a 100644
--- a/mp4.c
+++ b/mp4.c
@@ -13,7 +13,23 @@
 #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 {
+	/* determines which atoms we still need to parse. */
+	enum audio_track_state state;
+
 	/* mp4a */
 	uint16_t channel_count;
 	uint16_t sample_rate;
@@ -41,11 +57,8 @@ struct mp4_track {
 	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;
@@ -57,22 +70,13 @@ 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)
 {
@@ -82,8 +86,7 @@ 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;
@@ -94,7 +97,7 @@ 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;
 }
@@ -104,41 +107,21 @@ 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)
-{
-	uint8_t data[1];
-	int ret = read_data(f, data, 1);
-
-	if (ret > 0 && result)
-		*result = data[0];
-	return ret;
-}
-
 #define ATOM_ITEMS \
 	ATOM_ITEM(MOOV, 'm', 'o', 'o', 'v') \
 	ATOM_ITEM(TRAK, 't', 'r', 'a', 'k') \
@@ -205,41 +188,35 @@ 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);
 	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;
@@ -249,8 +226,8 @@ static int read_stsz(struct mp4 *f)
 	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]);
+	for (uint32_t n = 0; n < t->stsz_sample_count; n++) {
+		ret = read_int32(f, &t->stsz_table[n]);
 		if (ret <= 0)
 			return ret;
 	}
@@ -260,32 +237,21 @@ 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 */
+	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;
 }
@@ -293,35 +259,27 @@ 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]);
-		if (ret <= 0)
-			return ret;
-		ret = read_int32(f, &t->stsc_samples_per_chunk[i]);
+	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, 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;
 }
@@ -329,90 +287,36 @@ 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]);
+	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->channel_count);
-	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->sample_rate);
-}
-
 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;
@@ -420,9 +324,17 @@ 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);
 	}
@@ -463,16 +375,8 @@ 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);
@@ -484,13 +388,12 @@ static int parse_tag(struct mp4 *f, uint8_t parent, int32_t size)
 		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:
@@ -502,37 +405,25 @@ 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;
+		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;
+		skip_bytes(f, 8); /* creation time (4), modification time (4) */
 		ret = read_int32(f, &t->time_scale);
 		if (ret <= 0)
 			return ret;
@@ -542,16 +433,11 @@ 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;
@@ -580,19 +466,14 @@ 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)
@@ -652,15 +533,13 @@ static int parse_sub_atoms(struct mp4 *f, uint64_t total_size, bool meta_only)
 		if (ret <= 0)
 			return ret;
 		if (size == 0)
-			return -1;
+			return -E_MP4_CORRUPT;
 		dest = get_position(f) + size - header_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) {
+		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;
 		}
@@ -687,6 +566,21 @@ static int parse_sub_atoms(struct mp4 *f, uint64_t total_size, bool meta_only)
 	return 1;
 }
 
+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;
@@ -696,7 +590,6 @@ static int open_file(const struct mp4_callback *cb, bool meta_only, struct mp4 *
 
 	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);
@@ -708,62 +601,61 @@ 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)
+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
@@ -778,16 +670,14 @@ static int32_t chunk_of_sample(const struct mp4 *f, int32_t sample,
  */
 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->time_scale == 0)
-		return 0;
 	return t->duration * 1000 / t->time_scale;
 }
 
-int mp4_set_sample_position(struct mp4 *f, int32_t sample)
+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 */
 
@@ -810,34 +700,32 @@ 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)
+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)
+uint16_t mp4_get_sample_rate(const struct mp4 *f)
 {
-	return f->audio_track->sample_rate;
+	return f->track.sample_rate;
 }
 
-uint32_t mp4_get_channel_count(const struct mp4 *f)
+uint16_t mp4_get_channel_count(const struct mp4 *f)
 {
-	return f->audio_track->channel_count;
+	return f->track.channel_count;
 }
 
-int32_t mp4_num_samples(const struct mp4 *f)
+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;
 }
 
 int mp4_open_meta(const struct mp4_callback *cb, struct mp4 **result)
@@ -847,11 +735,6 @@ 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;
 }
@@ -907,7 +790,7 @@ 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 total_size = f->moov_size - 8;
 	uint32_t new_ilst_size = 0;
 	void *out_buffer;
 	uint8_t *p_out;
@@ -970,22 +853,26 @@ static void *modify_moov(struct mp4 *f, uint32_t *out_size)
 	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;
+	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)
+int mp4_update_meta(struct mp4 *f)
 {
 	void *new_moov_data;
 	uint32_t new_moov_size;
-	uint8_t buf[4];
+	uint8_t buf[8] = "----moov";
+	int ret;
 
 	set_position(f, 0);
 	new_moov_data = modify_moov(f, &new_moov_size);
@@ -995,83 +882,43 @@ int32_t mp4_meta_update(struct mp4 *f)
 	}
 	if (f->last_atom != ATOM_MOOV) {
 		set_position(f, f->moov_offset + 4);
-		write_data(f, "free", 4); /* rename old moov to free */
-		set_position(f, f->file_size); /* write new moov atom at EOF */
+		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_u32_be(buf, new_moov_size + 8);
-	write_data(f, buf, 4);
-	write_data(f, "moov", 4);
-	write_data(f, new_moov_data, new_moov_size);
+	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 ret;
 }
 
 /**
- * Return the value of the artist meta tag of an mp4 file.
+ * Return the value of the given tag item.
  *
  * \param f Must not be NULL.
+ * \param item "artist", "title", "album", "comment", or "date".
  *
- * \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.
+ * \return The function always 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_artist(const struct mp4 *f)
+char *mp4_get_tag_value(const struct mp4 *f, const char *item)
 {
-	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 the value of the album 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_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_meta_get_artist().
- * \return See \ref mp4_meta_get_artist().
- */
-char *mp4_meta_get_comment(const struct mp4 *f)
-{
-	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;
 }