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

[John Cox]

On Sat, 22 Jul 2023 17:28:31 +0200, you wrote:

>On Thu, Jul 20, 2023 at 1:40?PM John Cox <jc at kynesim.co.uk> wrote:
>
>> Add a callback to enable user allocation of video frames on the final
>> stage of a filter chain.
>>
>>
>What about an audio?
I have a use case for video and none for audio, but I can add audio if
you want.

>This works only for sinks mostly, what about filters inside graph?
Buffer allocation can already be set by the next filter in the chain
which is the callback I am tapping into. If you want to change that then
I guess the right answer would be to move get_buffer.video & audio out
of AVFilterPad and into somewhere publicly writeable, but I really don't
see the need. It seems sensible to me that buffer allocation internal to
graphs is negotiated between those filter elements and is opaque to the
user and it is only at the point where a buffer is delivered to the user
that the user needs to be able to intervene.

Regards

JC

>> Signed-off-by: John Cox <jc at 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
>> + * @param w width of frame to allocate
>> + * @param height of frame to allocate
>> + *
>> + * @return
>> + *         - The newly allocated frame
>> + *         - NULL if error
>> + */
>> +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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