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

[Marvin Scholz]

On 22 Jul 2023, at 21:10, John Cox wrote:

> On Sat, 22 Jul 2023 20:54:04 +0200, you wrote:
>
>> 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 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
>>
>> 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.
>
> Thanks - will do - Is documentation built from this? I had a quick look
> to see if I could find some output to verify what I'd done but I failed
> to find it.

You can generate it (if you have doxygen installed) by running:

make apidoc

and it will end up in doc/doxy/html.

>
>>> + * @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
>
> Will do.
>
> Ta
>
> JC
>
>>> + */
>>> +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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