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Fixed bug 4855 - Add looping support for FLAC
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Michael Day

Attached is a patch for music_flac.c which adds looping support for FLAC files. It mirrors the behavior and interface of the OGG looping. When loop tags LOOPSTART, LOOPEND and/or LOOPLENGTH are present in the FLAC Vorbis comment metadata, the module will use those specified values when looping the file. (It also accepts LOOP-* and LOOP_*.) Loop points can be expressed as raw PCM sample positions or as time strings of the form HH:MM:SS.ss.
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@slouken
slouken committed Nov 17, 2019
1 parent 02749dd commit 20bcf62
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Showing 2 changed files with 159 additions and 20 deletions.
4 changes: 4 additions & 0 deletions CHANGES.txt
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@@ -1,3 +1,7 @@
2.0.5:
Michael Day - Sat Nov 16 22:11:29 PST 2019
* Added looping support for FLAC files

2.0.4:
Ozkan Sezer - Wed, 10 Oct 2018 14:56:10
* Removed smpeg support for mp3 music, now that it's replaced by libmpg123
Expand Down
175 changes: 155 additions & 20 deletions music_flac.c
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Expand Up @@ -61,6 +61,11 @@ typedef struct {
FLAC__uint64 sample);
FLAC__StreamDecoderState (*FLAC__stream_decoder_get_state)(
const FLAC__StreamDecoder *decoder);
FLAC__uint64 (*FLAC__stream_decoder_get_total_samples)(
const FLAC__StreamDecoder *decoder);
FLAC__bool (*FLAC__stream_decoder_set_metadata_respond)(
FLAC__StreamDecoder *decoder,
FLAC__MetadataType type);
} flac_loader;

static flac_loader flac = {
Expand Down Expand Up @@ -114,6 +119,11 @@ static int FLAC_Load(void)
FUNCTION_LOADER(FLAC__stream_decoder_process_until_end_of_stream, FLAC__bool (*)(FLAC__StreamDecoder *))
FUNCTION_LOADER(FLAC__stream_decoder_seek_absolute, FLAC__bool (*)(FLAC__StreamDecoder *, FLAC__uint64))
FUNCTION_LOADER(FLAC__stream_decoder_get_state, FLAC__StreamDecoderState (*)(const FLAC__StreamDecoder *decoder))
FUNCTION_LOADER(FLAC__stream_decoder_get_total_samples,
FLAC__uint64 (*)(const FLAC__StreamDecoder *))
FUNCTION_LOADER(FLAC__stream_decoder_set_metadata_respond,
FLAC__bool (*)(FLAC__StreamDecoder *,
FLAC__MetadataType))
}
++flac.loaded;

Expand Down Expand Up @@ -144,6 +154,12 @@ typedef struct {
SDL_RWops *src;
int freesrc;
SDL_AudioStream *stream;
int loop;
FLAC__uint64 pcm_pos;
SDL_bool loop_flag;
FLAC__uint64 loop_start;
FLAC__uint64 loop_end;
FLAC__uint64 loop_len;
} FLAC_Music;


Expand Down Expand Up @@ -251,7 +267,7 @@ static FLAC__StreamDecoderWriteStatus flac_write_music_cb(
FLAC_Music *music = (FLAC_Music *)client_data;
Sint16 *data;
unsigned int i, j, channels;
int shift_amount = 0;
int shift_amount = 0, amount;

if (!music->stream) {
return FLAC__STREAM_DECODER_WRITE_STATUS_ABORT;
Expand Down Expand Up @@ -321,41 +337,124 @@ static FLAC__StreamDecoderWriteStatus flac_write_music_cb(
}
}
}
SDL_AudioStreamPut(music->stream, data, (frame->header.blocksize * channels * sizeof(*data)));
amount = frame->header.blocksize * channels * sizeof(*data);
music->pcm_pos += frame->header.blocksize;
if ((music->loop == 1) && (music->pcm_pos >= music->loop_end)) {
amount -= (music->pcm_pos - music->loop_end) * channels * sizeof(*data);
music->loop_flag = SDL_TRUE;
}

SDL_AudioStreamPut(music->stream, data, amount);
SDL_stack_free(data);

return FLAC__STREAM_DECODER_WRITE_STATUS_CONTINUE;
}

/* Parse time string of the form HH:MM:SS.mmm and return equivalent sample
* position */
static FLAC__uint64 parse_time(char *time, unsigned samplerate_hz)
{
char *num_start, *p;
FLAC__uint64 result = 0;
char c;

/* Time is directly expressed as a sample position */
if (SDL_strchr(time, ':') == NULL) {
return SDL_strtoull(time, NULL, 10);
}

result = 0;
num_start = time;

for (p = time; *p != '\0'; ++p) {
if (*p == '.' || *p == ':') {
c = *p; *p = '\0';
result = result * 60 + SDL_atoi(num_start);
num_start = p + 1;
*p = c;
}

if (*p == '.') {
return result * samplerate_hz
+ (FLAC__uint64) (SDL_atof(p) * samplerate_hz);
}
}

return (result * 60 + SDL_atoi(num_start)) * samplerate_hz;
}

static void flac_metadata_music_cb(
const FLAC__StreamDecoder *decoder,
const FLAC__StreamMetadata *metadata,
void *client_data)
{
FLAC_Music *music = (FLAC_Music *)client_data;
const FLAC__StreamMetadata_VorbisComment *vc;
int channels;
unsigned rate;
char *param, *argument, *value;
SDL_bool is_loop_length = SDL_FALSE;

if (metadata->type == FLAC__METADATA_TYPE_STREAMINFO) {
music->sample_rate = metadata->data.stream_info.sample_rate;
music->channels = metadata->data.stream_info.channels;
music->bits_per_sample = metadata->data.stream_info.bits_per_sample;
/*printf("FLAC: Sample rate = %d, channels = %d, bits_per_sample = %d\n", music->sample_rate, music->channels, music->bits_per_sample);*/

/* SDL's channel mapping and FLAC channel mapping are the same,
except for 3 channels: SDL is FL FR LFE and FLAC is FL FR FC
*/
if (music->channels == 3) {
channels = 2;
} else {
channels = music->channels;
}

if (metadata->type != FLAC__METADATA_TYPE_STREAMINFO) {
return;
}
/* We check for NULL stream later when we get data */
SDL_assert(!music->stream);
music->stream = SDL_NewAudioStream(AUDIO_S16SYS, channels, music->sample_rate,
music_spec.format, music_spec.channels, music_spec.freq);
} else if (metadata->type == FLAC__METADATA_TYPE_VORBIS_COMMENT) {
vc = &metadata->data.vorbis_comment;
rate = music->sample_rate;

for (int i = 0; i < vc->num_comments; ++i) {
param = SDL_strdup(vc->comments[i].entry);
argument = param;
value = SDL_strchr(param, '=');

if (value == NULL) {
value = param + SDL_strlen(param);
} else {
*(value++) = '\0';
}

music->sample_rate = metadata->data.stream_info.sample_rate;
music->channels = metadata->data.stream_info.channels;
music->bits_per_sample = metadata->data.stream_info.bits_per_sample;
/*printf("FLAC: Sample rate = %d, channels = %d, bits_per_sample = %d\n", music->sample_rate, music->channels, music->bits_per_sample);*/
/* Want to match LOOP-START, LOOP_START, etc. Remove - or _ from
* string if it is present at position 4. */

/* SDL's channel mapping and FLAC channel mapping are the same,
except for 3 channels: SDL is FL FR LFE and FLAC is FL FR FC
*/
if (music->channels == 3) {
channels = 2;
} else {
channels = music->channels;
if ((argument[4] == '_') || (argument[4] == '-')) {
SDL_memmove(argument + 4, argument + 5,
SDL_strlen(argument) - 4);
}

if (SDL_strcasecmp(argument, "LOOPSTART") == 0)
music->loop_start = parse_time(value, rate);
else if (SDL_strcasecmp(argument, "LOOPLENGTH") == 0) {
music->loop_len = SDL_strtoull(value, NULL, 10);
is_loop_length = SDL_TRUE;
} else if (SDL_strcasecmp(argument, "LOOPEND") == 0) {
is_loop_length = SDL_FALSE;
music->loop_end = parse_time(value, rate);
}
SDL_free(param);
}

if (is_loop_length) {
music->loop_end = music->loop_start + music->loop_len;
} else {
music->loop_len = music->loop_end - music->loop_start;
}
}
/* We check for NULL stream later when we get data */
SDL_assert(!music->stream);
music->stream = SDL_NewAudioStream(AUDIO_S16SYS, channels, music->sample_rate,
music_spec.format, music_spec.channels, music_spec.freq);
}

static void flac_error_music_cb(
Expand Down Expand Up @@ -389,6 +488,7 @@ static void *FLAC_CreateFromRW(SDL_RWops *src, int freesrc)
FLAC_Music *music;
int init_stage = 0;
int was_error = 1;
FLAC__uint64 full_length;

music = (FLAC_Music *)SDL_calloc(1, sizeof(*music));
if (!music) {
Expand All @@ -397,10 +497,18 @@ static void *FLAC_CreateFromRW(SDL_RWops *src, int freesrc)
}
music->src = src;
music->volume = MIX_MAX_VOLUME;
music->loop = -1;
music->loop_start = -1;
music->loop_end = 0;
music->loop_len = 0;
music->loop_flag = SDL_FALSE;
music->pcm_pos = 0;

music->flac_decoder = flac.FLAC__stream_decoder_new();
if (music->flac_decoder) {
init_stage++; /* stage 1! */
flac.FLAC__stream_decoder_set_metadata_respond(music->flac_decoder,
FLAC__METADATA_TYPE_VORBIS_COMMENT);

if (flac.FLAC__stream_decoder_init_stream(
music->flac_decoder,
Expand Down Expand Up @@ -436,6 +544,20 @@ static void *FLAC_CreateFromRW(SDL_RWops *src, int freesrc)
return NULL;
}

/* loop_start, loop_end and loop_len get set by metadata callback if tags
* are present in metadata.
*/

full_length = flac.FLAC__stream_decoder_get_total_samples(music->flac_decoder);
if (((music->loop_start >= 0) || (music->loop_end > 0)) &&
((music->loop_start < music->loop_end) || (music->loop_end > 0)) &&
(music->loop_start < full_length) &&
(music->loop_end <= full_length)) {
if (music->loop_start < 0) music->loop_start = 0;
if (music->loop_end == 0) music->loop_end = full_length;
music->loop = 1;
}

music->freesrc = freesrc;
return music;
}
Expand Down Expand Up @@ -477,6 +599,18 @@ static int FLAC_GetSome(void *context, void *data, int bytes, SDL_bool *done)
return -1;
}

if (music->loop_flag) {
music->pcm_pos = music->loop_start;
if (flac.FLAC__stream_decoder_seek_absolute(music->flac_decoder, music->loop_start) ==
FLAC__STREAM_DECODER_SEEK_ERROR) {
SDL_SetError("FLAC__stream_decoder_seek_absolute() failed");
flac.FLAC__stream_decoder_flush(music->flac_decoder);
return -1;
} else {
music->loop_flag = SDL_FALSE;
}
}

if (flac.FLAC__stream_decoder_get_state(music->flac_decoder) == FLAC__STREAM_DECODER_END_OF_STREAM) {
if (music->play_count == 1) {
music->play_count = 0;
Expand Down Expand Up @@ -507,6 +641,7 @@ static int FLAC_Seek(void *context, double position)
FLAC_Music *music = (FLAC_Music *)context;
double seek_sample = music->sample_rate * position;

music->pcm_pos = seek_sample;
if (!flac.FLAC__stream_decoder_seek_absolute(music->flac_decoder, (FLAC__uint64)seek_sample)) {
if (flac.FLAC__stream_decoder_get_state(music->flac_decoder) == FLAC__STREAM_DECODER_SEEK_ERROR) {
flac.FLAC__stream_decoder_flush(music->flac_decoder);
Expand Down

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