Re: [FFmpeg-devel] [PATCH v2 1/1] avfilter/buffersink: Add video frame allocation callback

[Marvin Scholz <epirat07@gmail.com>]

On 22 Jul 2023, at 18:41, John Cox wrote:

> Add a callback to enable user allocation of video frames on the final
> stage of a filter chain.
>
> Signed-off-by: John Cox <jc@kynesim.co.uk>
> ---
>  libavfilter/buffersink.c | 21 +++++++++++++++++++++
>  libavfilter/buffersink.h | 27 +++++++++++++++++++++++++++
>  libavfilter/version.h    |  2 +-
>  3 files changed, 49 insertions(+), 1 deletion(-)
>
> diff --git a/libavfilter/buffersink.c b/libavfilter/buffersink.c
> index 306c283f77..070b743186 100644
> --- a/libavfilter/buffersink.c
> +++ b/libavfilter/buffersink.c
> @@ -62,6 +62,11 @@ typedef struct BufferSinkContext {
>      int sample_rates_size;
>
>      AVFrame *peeked_frame;
> +
> +    union {
> +        av_buffersink_alloc_video_frame * video;
> +    } alloc_cb;
> +    void * alloc_v;
>  } BufferSinkContext;
>
>  #define NB_ITEMS(list) (list ## _size / sizeof(*list))
> @@ -154,6 +159,21 @@ int attribute_align_arg av_buffersink_get_samples(AVFilterContext *ctx,
>      return get_frame_internal(ctx, frame, 0, nb_samples);
>  }
>
> +static AVFrame * alloc_video_buffer(AVFilterLink *link, int w, int h)
> +{
> +    AVFilterContext * const ctx = link->dst;
> +    BufferSinkContext * const bs = ctx->priv;
> +    return bs->alloc_cb.video ? bs->alloc_cb.video(ctx, bs->alloc_v, w, h) :
> +        ff_default_get_video_buffer(link, w, h);
> +}
> +
> +void av_buffersink_set_alloc_video_frame(AVFilterContext *ctx, av_buffersink_alloc_video_frame * cb, void * v)
> +{
> +    BufferSinkContext * const bs = ctx->priv;
> +    bs->alloc_cb.video = cb;
> +    bs->alloc_v = v;
> +}
> +
>  static av_cold int common_init(AVFilterContext *ctx)
>  {
>      BufferSinkContext *buf = ctx->priv;
> @@ -381,6 +401,7 @@ static const AVFilterPad avfilter_vsink_buffer_inputs[] = {
>      {
>          .name = "default",
>          .type = AVMEDIA_TYPE_VIDEO,
> +        .get_buffer = {.video = alloc_video_buffer},
>      },
>  };
>
> diff --git a/libavfilter/buffersink.h b/libavfilter/buffersink.h
> index 64e08de53e..73f0ddc476 100644
> --- a/libavfilter/buffersink.h
> +++ b/libavfilter/buffersink.h
> @@ -166,6 +166,33 @@ int av_buffersink_get_frame(AVFilterContext *ctx, AVFrame *frame);
>   */
>  int av_buffersink_get_samples(AVFilterContext *ctx, AVFrame *frame, int nb_samples);
>
> +/**
> + * Callback from av_buffersink_set_alloc_video_frame to allocate
> + * a frame
> + *
> + * @param ctx pointer to a context of the abuffersink AVFilter.
> + * @param v opaque pointer passed to
> + *          av_buffersink_set_alloc_video_frame

Nit:

You can use @ref av_buffersink_set_alloc_video_frame  or even
shorter ::av_buffersink_set_alloc_video_frame to get a proper
reference to that function that will be linked.

> + * @param w width of frame to allocate
> + * @param height of frame to allocate
> + *
> + * @return
> + *         - The newly allocated frame
> + *         - NULL if error

Nit:

This can use retval, for example like that:

@retval AVFrame* The newly allocated frame
@retval NULL     Error allocating the frame

> + */
> +typedef AVFrame * av_buffersink_alloc_video_frame(AVFilterContext * ctx, void * v, int w, int h);
> +
> +/**
> + * Set a video frame allocation method for buffersink
> + *
> + * @param ctx pointer to a context of the abuffersink AVFilter.
> + * @param cb Callback to the allocation function. If set to NULL
> + *           then the default avfilter allocation function will
> + *           be used.
> + * @param v  Opaque to pass to the allocation function
> + */
> +void av_buffersink_set_alloc_video_frame(AVFilterContext *ctx, av_buffersink_alloc_video_frame * cb, void * v);
> +
>  /**
>   * @}
>   */
> diff --git a/libavfilter/version.h b/libavfilter/version.h
> index c001693e3c..54950497be 100644
> --- a/libavfilter/version.h
> +++ b/libavfilter/version.h
> @@ -31,7 +31,7 @@
>
>  #include "version_major.h"
>
> -#define LIBAVFILTER_VERSION_MINOR   8
> +#define LIBAVFILTER_VERSION_MINOR   9
>  #define LIBAVFILTER_VERSION_MICRO 102
>
>
> -- 
> 2.39.2
>
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