X-Git-Url: http://git.tuebingen.mpg.de/?a=blobdiff_plain;f=mp4.c;h=f576529c0a954967e327834ae2b4e0bd204f24e2;hb=3fecc9a4654398b856f5722af298aa61f9407d9f;hp=8d58c1f2b58270371808e020eb0f5eb9855b9b26;hpb=9f41e0a646faa238673bfdbe4dbdccb9cea37b7d;p=paraslash.git

diff --git a/mp4.c b/mp4.c
index 8d58c1f2..f576529c 100644
--- a/mp4.c
+++ b/mp4.c
@@ -15,12 +15,8 @@
 struct mp4_track {
 	bool is_audio;
 	int32_t channelCount;
-	int32_t sampleSize;
 	uint16_t sampleRate;
 
-	/* stsd */
-	int32_t stsd_entry_count;
-
 	/* stsz */
 	int32_t stsz_sample_size;
 	int32_t stsz_sample_count;
@@ -41,14 +37,6 @@ struct mp4_track {
 	int32_t stco_entry_count;
 	int32_t *stco_chunk_offset;
 
-	/* ctts */
-	int32_t ctts_entry_count;
-	int32_t *ctts_sample_count;
-	int32_t *ctts_sample_offset;
-
-	uint32_t maxBitrate;
-	uint32_t avgBitrate;
-
 	uint32_t timeScale;
 	uint64_t duration;
 };
@@ -56,14 +44,15 @@ struct mp4_track {
 #define MAX_TRACKS 1024
 
 struct mp4 {
-	/* stream to read from */
-	struct mp4_callback *stream;
+	const struct mp4_callback *cb;
 	int64_t current_position;
 
 	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 */
@@ -85,10 +74,10 @@ static int32_t read_data(struct mp4 *f, void *data, uint32_t size)
 {
 	int32_t result = 1;
 
-	result = f->stream->read(f->stream->user_data, data, size);
+	result = f->cb->read(f->cb->user_data, data, size);
 
 	if (result < size)
-		f->stream->read_error++;
+		f->read_error++;
 
 	f->current_position += size;
 
@@ -108,7 +97,6 @@ static bool atom_compare(int8_t a1, int8_t b1, int8_t c1, int8_t d1,
 {
 	return a1 == a2 && b1 == b2 && c1 == c2 && d1 == d2;
 }
-
 enum atoms {
 	/* atoms with subatoms */
 	ATOM_MOOV = 1,
@@ -400,7 +388,7 @@ static int need_parse_when_meta_only(uint8_t atom_type)
 
 static int32_t set_position(struct mp4 *f, int64_t position)
 {
-	f->stream->seek(f->stream->user_data, position);
+	f->cb->seek(f->cb->user_data, position);
 	f->current_position = position;
 
 	return 0;
@@ -456,7 +444,7 @@ static int32_t read_stsz(struct mp4 *f)
 	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->stream->read_error; i++)
+	for (i = 0; i < t->stsz_sample_count && !f->read_error; i++)
 		t->stsz_table[i] = read_int32(f);
 	return 0;
 }
@@ -481,41 +469,13 @@ static int32_t read_stts(struct mp4 *f)
 	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->stream->read_error; i++) {
+	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;
 }
 
-static int32_t read_ctts(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];
-	if (t->ctts_entry_count)
-		return 0;
-
-	read_char(f);	/* version */
-	read_int24(f);	/* flags */
-	t->ctts_entry_count = read_int32(f);
-
-	t->ctts_sample_count = para_malloc(t->ctts_entry_count
-		* sizeof (int32_t));
-	t->ctts_sample_offset = para_malloc(t->ctts_entry_count
-		* sizeof (int32_t));
-
-	/* CVE-2017-9257 */
-	for (i = 0; i < t->ctts_entry_count && !f->stream->read_error; i++) {
-		t->ctts_sample_count[i] = read_int32(f);
-		t->ctts_sample_offset[i] = read_int32(f);
-	}
-	return 1;
-}
-
 static int32_t read_stsc(struct mp4 *f)
 {
 	int32_t i;
@@ -535,7 +495,7 @@ static int32_t read_stsc(struct mp4 *f)
 		sizeof (int32_t));
 
 	/* CVE-2017-9255 */
-	for (i = 0; i < t->stsc_entry_count && !f->stream->read_error; i++) {
+	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);
@@ -558,7 +518,7 @@ static int32_t read_stco(struct mp4 *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->stream->read_error; i++)
+	for (i = 0; i < t->stco_entry_count && !f->read_error; i++)
 		t->stco_chunk_offset[i] = read_int32(f);
 	return 0;
 }
@@ -591,7 +551,7 @@ static int32_t read_mp4a(struct mp4 *f)
 	read_int32(f);	/* reserved */
 
 	t->channelCount = read_int16(f);
-	t->sampleSize = read_int16(f);
+	read_int16(f);
 
 	read_int16(f);
 	read_int16(f);
@@ -606,7 +566,7 @@ static int32_t read_mp4a(struct mp4 *f)
 
 static int32_t read_stsd(struct mp4 *f)
 {
-	int32_t i;
+	int32_t i, entry_count;
 	uint8_t header_size = 0;
 	struct mp4_track *t;
 
@@ -618,10 +578,10 @@ static int32_t read_stsd(struct mp4 *f)
 	read_char(f);	/* version */
 	read_int24(f);	/* flags */
 
-	t->stsd_entry_count = read_int32(f);
+	entry_count = read_int32(f);
 
 	/* CVE-2017-9253 */
-	for (i = 0; i < t->stsd_entry_count && !f->stream->read_error; i++) {
+	for (i = 0; i < entry_count && !f->read_error; i++) {
 		uint64_t skip = get_position(f);
 		uint64_t size;
 		uint8_t atom_type = 0;
@@ -639,8 +599,6 @@ static int32_t read_stsd(struct mp4 *f)
 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);
@@ -687,15 +645,6 @@ static const char *ID3v1GenreList[] = {
 	"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);
@@ -707,232 +656,47 @@ static char *read_string(struct mp4 *f, uint32_t length)
 	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 void parse_tag(struct mp4 *f, uint8_t parent, int32_t size)
 {
-	uint8_t atom_type;
-	uint8_t header_size = 0;
 	uint64_t subsize, sumsize;
-	char *name = NULL;
 	char *data = NULL;
-	uint32_t done = 0;
 	uint32_t len = 0;
 	uint64_t destpos;
 
 	for (
 		sumsize = 0;
-		sumsize < size && !f->stream->read_error; /* CVE-2017-9222 */
+		sumsize < size && !f->read_error; /* CVE-2017-9222 */
 		set_position(f, destpos), sumsize += subsize
 	) {
+		uint8_t atom_type;
+		uint8_t header_size = 0;
 		subsize = atom_read_header(f, &atom_type, &header_size);
 		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);
-		}
-	}
-	if (data) {
-		if (!done) {
-			if (name == NULL)
-				set_metadata_name(parent , &name);
-			if (name)
-				tag_add_field(&(f->tags), name, data, len);
-		}
-
 		free(data);
+		data = read_string(f, subsize - (header_size + 8));
+		len = subsize - (header_size + 8);
 	}
-	free(name);
-	return 1;
+	if (!data)
+		return;
+	tag_add_field(&f->tags, get_metadata_name(parent), data, len);
+	free(data);
 }
 
 static int32_t read_mdhd(struct mp4 *f)
@@ -968,15 +732,25 @@ static int32_t read_mdhd(struct mp4 *f)
 
 static int32_t parse_metadata(struct mp4 *f, int32_t size)
 {
-	uint64_t subsize, sumsize = 0;
-	uint8_t atom_type;
-	uint8_t header_size = 0;
+	uint64_t sumsize = 0;
 
 	while (sumsize < size) {
+		uint8_t atom_type;
+		uint64_t subsize, destpos;
+		uint8_t header_size = 0;
 		subsize = atom_read_header(f, &atom_type, &header_size);
 		if (subsize == 0)
 			break;
-		parse_tag(f, atom_type, (uint32_t)(subsize - header_size));
+		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:
+			parse_tag(f, atom_type, subsize - header_size);
+		}
+		set_position(f, destpos);
 		sumsize += subsize;
 	}
 
@@ -1016,9 +790,6 @@ static int32_t atom_read(struct mp4 *f, int32_t size, uint8_t atom_type)
 	} else if (atom_type == ATOM_STTS) {
 		/* time to sample box */
 		read_stts(f);
-	} else if (atom_type == ATOM_CTTS) {
-		/* composition offset box */
-		read_ctts(f);
 	} else if (atom_type == ATOM_STSC) {
 		/* sample to chunk box */
 		read_stsc(f);
@@ -1082,7 +853,7 @@ static int32_t parse_atoms(struct mp4 *f, int meta_only)
 	uint8_t header_size = 0;
 
 	f->file_size = 0;
-	f->stream->read_error = 0;
+	f->read_error = 0;
 
 	while ((size =
 		atom_read_header(f, &atom_type, &header_size)) != 0) {
@@ -1108,20 +879,17 @@ static int32_t parse_atoms(struct mp4 *f, int meta_only)
 	return 0;
 }
 
-struct mp4 *mp4_open_read(struct mp4_callback *f)
+struct mp4 *mp4_open_read(const struct mp4_callback *cb)
 {
-	struct mp4 *ff = para_calloc(sizeof(struct mp4));
-
-	ff->stream = f;
+	struct mp4 *f = para_calloc(sizeof(struct mp4));
 
-	parse_atoms(ff, 0);
-
-	if (ff->error) {
-		free(ff);
-		ff = NULL;
+	f->cb = cb;
+	parse_atoms(f, 0);
+	if (f->error) {
+		free(f);
+		f = NULL;
 	}
-
-	return ff;
+	return f;
 }
 
 static int32_t tag_delete(struct mp4_metadata *tags)
@@ -1139,27 +907,25 @@ static int32_t tag_delete(struct mp4_metadata *tags)
 	return 0;
 }
 
-void mp4_close(struct mp4 *ff)
+void mp4_close(struct mp4 *f)
 {
 	int32_t i;
 
-	for (i = 0; i < ff->total_tracks; i++) {
-		if (ff->track[i]) {
-			free(ff->track[i]->stsz_table);
-			free(ff->track[i]->stts_sample_count);
-			free(ff->track[i]->stts_sample_delta);
-			free(ff->track[i]->stsc_first_chunk);
-			free(ff->track[i]->stsc_samples_per_chunk);
-			free(ff->track[i]->stsc_sample_desc_index);
-			free(ff->track[i]->stco_chunk_offset);
-			free(ff->track[i]->ctts_sample_count);
-			free(ff->track[i]->ctts_sample_offset);
-			free(ff->track[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]);
 		}
 	}
 
-	tag_delete(&(ff->tags));
-	free(ff);
+	tag_delete(&(f->tags));
+	free(f);
 }
 
 static int32_t chunk_of_sample(const struct mp4 *f, int32_t track,
@@ -1326,20 +1092,17 @@ int32_t mp4_num_samples(const struct mp4 *f, int32_t track)
 	return total;
 }
 
-struct mp4 *mp4_open_meta(struct mp4_callback *f)
+struct mp4 *mp4_open_meta(const struct mp4_callback *cb)
 {
-	struct mp4 *ff = para_calloc(sizeof(struct mp4));
-
-	ff->stream = f;
+	struct mp4 *f = para_calloc(sizeof(struct mp4));
 
-	parse_atoms(ff, 1);
-
-	if (ff->error) {
-		free(ff);
-		ff = NULL;
+	f->cb = cb;
+	parse_atoms(f, 1);
+	if (f->error) {
+		free(f);
+		f = NULL;
 	}
-
-	return ff;
+	return f;
 }
 
 int32_t mp4_meta_get_num_items(const struct mp4 *f)
@@ -1932,7 +1695,7 @@ static int32_t write_data(struct mp4 *f, void *data, uint32_t size)
 {
 	int32_t result = 1;
 
-	result = f->stream->write(f->stream->user_data, data, size);
+	result = f->cb->write(f->cb->user_data, data, size);
 
 	f->current_position += size;
 
@@ -1946,93 +1709,108 @@ static int32_t write_int32(struct mp4 *f, uint32_t data)
 	return write_data(f, temp, sizeof(temp));
 }
 
-static int32_t truncate_stream(struct mp4 *f)
-{
-	return f->stream->truncate(f->stream->user_data);
-}
-
-int32_t mp4_meta_update(struct mp4_callback *f, const struct mp4_metadata *data)
+int32_t mp4_meta_update(const struct mp4_callback *cb,
+		const struct mp4_metadata *data)
 {
 	void *new_moov_data;
 	uint32_t new_moov_size;
 
-	struct mp4 *ff = para_calloc(sizeof(struct mp4));
-	ff->stream = f;
-	set_position(ff, 0);
-
-	parse_atoms(ff, 1);
-
-	if (!modify_moov(ff, data, &new_moov_data, &new_moov_size)) {
-		mp4_close(ff);
+	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)) {
+		mp4_close(f);
 		return 0;
 	}
 
 	/* copy moov atom to end of the file */
-	if (ff->last_atom != ATOM_MOOV) {
+	if (f->last_atom != ATOM_MOOV) {
 		char *free_data = "free";
 
 		/* rename old moov to free */
-		set_position(ff, ff->moov_offset + 4);
-		write_data(ff, free_data, 4);
+		set_position(f, f->moov_offset + 4);
+		write_data(f, free_data, 4);
 
-		set_position(ff, ff->file_size);
-		write_int32(ff, new_moov_size + 8);
-		write_data(ff, "moov", 4);
-		write_data(ff, new_moov_data, new_moov_size);
+		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 {
-		set_position(ff, ff->moov_offset);
-		write_int32(ff, new_moov_size + 8);
-		write_data(ff, "moov", 4);
-		write_data(ff, new_moov_data, new_moov_size);
+		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);
 	}
-
-	truncate_stream(ff);
-
-	mp4_close(ff);
+	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)
+static char *meta_find_by_name(const struct mp4 *f, const char *item)
 {
 	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;
+	for (i = 0; i < f->tags.count; i++)
+		if (!strcasecmp(f->tags.tags[i].item, item))
+			return para_strdup(f->tags.tags[i].value);
+	return NULL;
 }
 
-int32_t mp4_meta_get_artist(const struct mp4 *f, char **value)
+/**
+ * Return the value of the artist meta tag of an mp4 file.
+ *
+ * \param f Must not be NULL.
+ *
+ * \return If the file does not contain this metadata tag, the function returns
+ * NULL. Otherwise, a copy of the tag value is returned. The caller should free
+ * this memory when it is no longer needed.
+ */
+char *mp4_meta_get_artist(const struct mp4 *f)
 {
-	return meta_find_by_name(f, "artist", value);
+	return meta_find_by_name(f, "artist");
 }
 
-int32_t mp4_meta_get_title(const struct mp4 *f, char **value)
+/**
+ * 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", value);
+	return meta_find_by_name(f, "title");
 }
 
-int32_t mp4_meta_get_date(const struct mp4 *f, char **value)
+/**
+ * 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", value);
+	return meta_find_by_name(f, "date");
 }
 
-int32_t mp4_meta_get_album(const struct mp4 *f, char **value)
+/**
+ * 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", value);
+	return meta_find_by_name(f, "album");
 }
 
-int32_t mp4_meta_get_comment(const struct mp4 *f, char **value)
+/**
+ * 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", value);
+	return meta_find_by_name(f, "comment");
 }