Re: [FFmpeg-devel] [PATCH 3/3] avcodec/av1_parser: use an AVBufferRef to avoid data copying

[Andreas Rheinhardt <andreas.rheinhardt@outlook.com>]

James Almer:
> Signed-off-by: James Almer <jamrial@gmail.com>
> ---
>  libavcodec/av1_parser.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/libavcodec/av1_parser.c b/libavcodec/av1_parser.c
> index 77906d0c91..b9a96ad59a 100644
> --- a/libavcodec/av1_parser.c
> +++ b/libavcodec/av1_parser.c
> @@ -50,6 +50,11 @@ static const enum AVPixelFormat pix_fmts_rgb[3] = {
>      AV_PIX_FMT_GBRP, AV_PIX_FMT_GBRP10, AV_PIX_FMT_GBRP12,
>  };
>  
> +static void dummy_free(void *opaque, uint8_t *data)
> +{
> +    av_assert0(opaque == data);
> +}
> +
>  static int av1_parser_parse(AVCodecParserContext *ctx,
>                              AVCodecContext *avctx,
>                              const uint8_t **out_data, int *out_size,
> @@ -60,6 +65,7 @@ static int av1_parser_parse(AVCodecParserContext *ctx,
>      const CodedBitstreamAV1Context *av1 = s->cbc->priv_data;
>      const AV1RawSequenceHeader *seq;
>      const AV1RawColorConfig *color;
> +    AVBufferRef *ref = NULL;
>      int ret;
>  
>      *out_data = data;
> @@ -69,6 +75,11 @@ static int av1_parser_parse(AVCodecParserContext *ctx,
>      ctx->pict_type         = AV_PICTURE_TYPE_NONE;
>      ctx->picture_structure = AV_PICTURE_STRUCTURE_UNKNOWN;
>  
> +    ref = av_buffer_create((uint8_t *)data, size, dummy_free,
> +                           (void *)data, AV_BUFFER_FLAG_READONLY);
> +    if (!ref)
> +        return size;
> +
>      s->cbc->log_ctx = avctx;
>  
>      if (avctx->extradata_size && !s->parsed_extradata) {
> @@ -171,6 +182,8 @@ static int av1_parser_parse(AVCodecParserContext *ctx,
>  
>  end:
>      ff_cbs_fragment_reset(td);
> +    av_assert1(av_buffer_get_ref_count(ref) == 1);
> +    av_buffer_unref(&ref);
>  
>      s->cbc->log_ctx = NULL;
>  

Lying to CBS (and the AVBuffer API) is an ugly hack which just happens
to work and relies on knowledge of the internals of CBS AV1. I very much
prefer my approach in
https://ffmpeg.org/pipermail/ffmpeg-devel/2025-May/343195.html (where
CBS is explicitly told of the desire not to create additional references).

- Andreas

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