* [FFmpeg-devel] [PATCH] avformat/wavdec: support loop_start and loop_end from 'smpl' chunk
@ 2025-08-30 23:27 Spencer Alves via ffmpeg-devel
2025-09-02 20:02 ` [FFmpeg-devel] " Michael Niedermayer via ffmpeg-devel
0 siblings, 1 reply; 2+ messages in thread
From: Spencer Alves via ffmpeg-devel @ 2025-08-30 23:27 UTC (permalink / raw)
To: ffmpeg-devel; +Cc: Spencer Alves
The 'smpl' chunk is used for sampling music synthesizers, and includes
things like the pitch of the sample and how to loop it. This exposes the
loop points as "loop_start" and "loop_end" metadata, that the brstm,
mca, and scd demuxers already support.
Tested with file output from "Polyphone" soundfont editor.
Signed-off-by: Spencer Alves <impiaaa@gmail.com>
---
libavformat/wavdec.c | 22 ++++++++++++++++++++++
1 file changed, 22 insertions(+)
diff --git a/libavformat/wavdec.c b/libavformat/wavdec.c
index c65e0a2723..fb3749d64d 100644
--- a/libavformat/wavdec.c
+++ b/libavformat/wavdec.c
@@ -595,6 +595,28 @@ static int wav_read_header(AVFormatContext *s)
}
}
break;
+ case MKTAG('s', 'm', 'p', 'l'):
+ if (size >= 36 && got_fmt && st->codecpar->sample_rate > 0) {
+ unsigned sample_loop_count;
+ avio_skip(pb, 28);
+ sample_loop_count = avio_rl32(pb);
+ avio_skip(pb, 4);
+ for (unsigned i = 0; i < sample_loop_count; i++) {
+ avio_skip(pb, 8);
+ if (av_dict_set_int(&s->metadata, "loop_start",
+ av_rescale(avio_rl32(pb), AV_TIME_BASE,
+ st->codecpar->sample_rate),
+ AV_DICT_MULTIKEY) < 0)
+ return AVERROR(ENOMEM);
+ avio_skip(pb, 8);
+ if (av_dict_set_int(&s->metadata, "loop_end",
+ av_rescale(avio_rl32(pb), AV_TIME_BASE,
+ st->codecpar->sample_rate),
+ AV_DICT_MULTIKEY) < 0)
+ return AVERROR(ENOMEM);
+ }
+ }
+ break;
}
/* seek to next tag unless we know that we'll run into EOF */
--
2.48.1
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^ permalink raw reply [flat|nested] 2+ messages in thread
* [FFmpeg-devel] Re: [PATCH] avformat/wavdec: support loop_start and loop_end from 'smpl' chunk
2025-08-30 23:27 [FFmpeg-devel] [PATCH] avformat/wavdec: support loop_start and loop_end from 'smpl' chunk Spencer Alves via ffmpeg-devel
@ 2025-09-02 20:02 ` Michael Niedermayer via ffmpeg-devel
0 siblings, 0 replies; 2+ messages in thread
From: Michael Niedermayer via ffmpeg-devel @ 2025-09-02 20:02 UTC (permalink / raw)
To: FFmpeg development discussions and patches; +Cc: Michael Niedermayer
[-- Attachment #1.1: Type: text/plain, Size: 2328 bytes --]
On Sat, Aug 30, 2025 at 04:27:25PM -0700, Spencer Alves via ffmpeg-devel wrote:
> The 'smpl' chunk is used for sampling music synthesizers, and includes
> things like the pitch of the sample and how to loop it. This exposes the
> loop points as "loop_start" and "loop_end" metadata, that the brstm, mca,
> and scd demuxers already support.
>
> Tested with file output from "Polyphone" soundfont editor.
>
> Signed-off-by: Spencer Alves <impiaaa@gmail.com>
> ---
> libavformat/wavdec.c | 22 ++++++++++++++++++++++
> 1 file changed, 22 insertions(+)
>
> diff --git a/libavformat/wavdec.c b/libavformat/wavdec.c
> index c65e0a2723..fb3749d64d 100644
> --- a/libavformat/wavdec.c
> +++ b/libavformat/wavdec.c
> @@ -595,6 +595,28 @@ static int wav_read_header(AVFormatContext *s)
> }
> }
> break;
> + case MKTAG('s', 'm', 'p', 'l'):
> + if (size >= 36 && got_fmt && st->codecpar->sample_rate > 0) {
> + unsigned sample_loop_count;
> + avio_skip(pb, 28);
> + sample_loop_count = avio_rl32(pb);
> + avio_skip(pb, 4);
> + for (unsigned i = 0; i < sample_loop_count; i++) {
> + avio_skip(pb, 8);
> + if (av_dict_set_int(&s->metadata, "loop_start",
> + av_rescale(avio_rl32(pb), AV_TIME_BASE,
> + st->codecpar->sample_rate),
> + AV_DICT_MULTIKEY) < 0)
> + return AVERROR(ENOMEM);
> + avio_skip(pb, 8);
> + if (av_dict_set_int(&s->metadata, "loop_end",
> + av_rescale(avio_rl32(pb), AV_TIME_BASE,
> + st->codecpar->sample_rate),
> + AV_DICT_MULTIKEY) < 0)
> + return AVERROR(ENOMEM);
> + }
> + }
> + break;
> }
> /* seek to next tag unless we know that we'll run into EOF */
> --
error: corrupt patch at line 38
[...]
--
Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
Opposition brings concord. Out of discord comes the fairest harmony.
-- Heraclitus
[-- Attachment #1.2: signature.asc --]
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[-- Attachment #2: Type: text/plain, Size: 163 bytes --]
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2025-08-30 23:27 [FFmpeg-devel] [PATCH] avformat/wavdec: support loop_start and loop_end from 'smpl' chunk Spencer Alves via ffmpeg-devel
2025-09-02 20:02 ` [FFmpeg-devel] " Michael Niedermayer via ffmpeg-devel
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