[FFmpeg-devel] Re: [PATCH] avformat/wavdec: support loop_start and loop_end from 'smpl' chunk

[Michael Niedermayer via ffmpeg-devel <ffmpeg-devel@ffmpeg.org>]

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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

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