Re: [FFmpeg-devel] [PATCH] avcodec/sbcenc: port to AVCodec.get_supported_config()

[Zhao Zhili <quinkblack-at-foxmail.com@ffmpeg.org>]

> On Feb 19, 2025, at 03:28, James Almer <jamrial@gmail.com> wrote:
> 
> Signed-off-by: James Almer <jamrial@gmail.com>
> ---
> libavcodec/sbcenc.c | 50 +++++++++++++++++++++++++++++++++++++--------
> 1 file changed, 41 insertions(+), 9 deletions(-)
> 
> diff --git a/libavcodec/sbcenc.c b/libavcodec/sbcenc.c
> index f2c4fbe329..d85ab76cb0 100644
> --- a/libavcodec/sbcenc.c
> +++ b/libavcodec/sbcenc.c
> @@ -194,6 +194,8 @@ static size_t sbc_pack_frame(AVPacket *avpkt, struct sbc_frame *frame,
>     return put_bytes_output(&pb);
> }
> 
> +static const int sbc_supported_samplerates[] = { 16000, 32000, 44100, 48000, 0 };
> +
> static int sbc_encode_init(AVCodecContext *avctx)
> {
>     SBCEncContext *sbc = avctx->priv_data;
> @@ -260,8 +262,8 @@ static int sbc_encode_init(AVCodecContext *avctx)
>         avctx->frame_size = 4*((frame->subbands >> 3) + 1) * 4*(frame->blocks >> 2);
>     }
> 
> -    for (int i = 0; avctx->codec->supported_samplerates[i]; i++)
> -        if (avctx->sample_rate == avctx->codec->supported_samplerates[i])
> +    for (int i = 0; sbc_supported_samplerates[i]; i++)
> +        if (avctx->sample_rate == sbc_supported_samplerates[i])
>             frame->frequency = i;
> 
>     frame->channels = avctx->ch_layout.nb_channels;
> @@ -326,6 +328,41 @@ static int sbc_encode_frame(AVCodecContext *avctx, AVPacket *avpkt,
>     return 0;
> }
> 
> +static const enum AVSampleFormat sbc_sample_fmts[] = {
> +   AV_SAMPLE_FMT_S16,
> +   AV_SAMPLE_FMT_NONE
> +};
> +
> +static const AVChannelLayout sbc_ch_layouts[] = {
> +    AV_CHANNEL_LAYOUT_MONO,
> +    AV_CHANNEL_LAYOUT_STEREO,
> +    { 0 }
> +};
> +
> +static int sbc_get_supported_config(const AVCodecContext *avctx,
> +                                    const AVCodec *codec,
> +                                    enum AVCodecConfig config,
> +                                    unsigned flags, const void **out,
> +                                    int *out_num)
> +{
> +    switch (config) {
> +    case AV_CODEC_CONFIG_SAMPLE_RATE:
> +        *out = sbc_supported_samplerates;
> +        *out_num = FF_ARRAY_ELEMS(sbc_supported_samplerates) - 1;
> +        return 0;
> +    case AV_CODEC_CONFIG_SAMPLE_FORMAT:
> +        *out = sbc_sample_fmts;
> +        *out_num = FF_ARRAY_ELEMS(sbc_sample_fmts) - 1;
> +        return 0;
> +    case AV_CODEC_CONFIG_CHANNEL_LAYOUT:
> +        *out = sbc_ch_layouts;
> +        *out_num = FF_ARRAY_ELEMS(sbc_ch_layouts) - 1;
> +        return 0;
> +    }
> +
> +    return ff_default_get_supported_config(avctx, codec, config, flags, out, out_num);
> +}
> +
> #define OFFSET(x) offsetof(SBCEncContext, x)
> #define AE AV_OPT_FLAG_AUDIO_PARAM | AV_OPT_FLAG_ENCODING_PARAM
> static const AVOption options[] = {
> @@ -344,7 +381,7 @@ static const AVClass sbc_class = {
>     .version    = LIBAVUTIL_VERSION_INT,
> };
> 
> -const FFCodec ff_sbc_encoder = {
> +FFCodec ff_sbc_encoder = {
>     .p.name                = "sbc",
>     CODEC_LONG_NAME("SBC (low-complexity subband codec)"),
>     .p.type                = AVMEDIA_TYPE_AUDIO,
> @@ -354,12 +391,7 @@ const FFCodec ff_sbc_encoder = {
>     .priv_data_size        = sizeof(SBCEncContext),
>     .init                  = sbc_encode_init,
>     FF_CODEC_ENCODE_CB(sbc_encode_frame),
> -    .p.ch_layouts          = (const AVChannelLayout[]) { AV_CHANNEL_LAYOUT_MONO,
> -                                                         AV_CHANNEL_LAYOUT_STEREO,
> -                                                         { 0 } },
> -    .p.sample_fmts         = (const enum AVSampleFormat[]) { AV_SAMPLE_FMT_S16,
> -                                                             AV_SAMPLE_FMT_NONE },
> -    .p.supported_samplerates = (const int[]) { 16000, 32000, 44100, 48000, 0 },
> +    .get_supported_config  = sbc_get_supported_config,
>     .p.priv_class          = &sbc_class,
>     .p.profiles            = NULL_IF_CONFIG_SMALL(ff_sbc_profiles),
> };

static fields works for most of the codecs. It’s not worth the complexity and code duplication
to implement get_supported_config just to silence the warning.

The issue has two parts:
1. Prepare to remove those fields inside libavcodec.
2. Silence the warning

For the first part, I prefer add those fields to FFCodec, e.g.,

https://ffmpeg.org/pipermail/ffmpeg-devel/2025-February/339330.html

https://ffmpeg.org/pipermail/ffmpeg-devel/2025-February/339335.html

This method doesn’t silence the warning.

For the second part, I have a non portable try

https://ffmpeg.org/pipermail/ffmpeg-devel/2025-February/339334.html

And Andreas pointed out how to make it portable.


> -- 
> 2.48.1
> 
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