[FFmpeg-devel] [PATCH v2] avcodec/cuviddec: update parser ulMaxNumDecodeSurfaces

[Timo Rothenpieler]

On 11.08.2023 19:50, Random Joe wrote:
> Fixes video output stutter caused by different number of buffers in
> decoder vs parser introduced in 402d98c.
> 
> Signed-off-by: Random Joe <ff.random.joe at gmail.com>
> ---
>   libavcodec/cuviddec.c | 13 +++++++++++--
>   1 file changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/libavcodec/cuviddec.c b/libavcodec/cuviddec.c
> index 814bc53f70..1b62832eca 100644
> --- a/libavcodec/cuviddec.c
> +++ b/libavcodec/cuviddec.c
> @@ -360,7 +360,14 @@ static int CUDAAPI cuvid_handle_video_sequence(void 
> *opaque, CUVIDEOFORMAT* form
>           }
>       }
> 
> -    return 1;
> +    // make CUVIDDECODECREATEINFO::ulNumDecodeSurfaces = 
> CUVIDPARSERPARAMS::ulMaxNumDecodeSurfaces
> +    // returning a value > 1  , will notify the driver to set the 
> parser ulMaxNumDecodeSurfaces
> +    // to this return value .
> +
> +    if(ctx->cuparseinfo.ulMaxNumDecodeSurfaces != 
> cuinfo.ulNumDecodeSurfaces)
> +        return cuinfo.ulNumDecodeSurfaces;
> +    else
> +        return 1;

Any reason to not just always return nb_surfaces here?
I don't really understand why this would cause stuttering though. It 
might waste a bit of memory to always set the maximum number to the 
allowed maximum, but why would it hurt performance?

>   }
> 
>   static int CUDAAPI cuvid_handle_picture_decode(void *opaque, 
> CUVIDPICPARAMS* picparams)
> @@ -1022,7 +1029,9 @@ static av_cold int 
> cuvid_decode_init(AVCodecContext *avctx)
>           goto error;
>       }
> 
> -    ctx->cuparseinfo.ulMaxNumDecodeSurfaces = ctx->nb_surfaces;
> +    // set ulMaxNumDecodeSurfaces to a dummy value of 1 as recommended 
> in NVDEC Programming Guide
> +    // set the optimal value in pfnSequenceCallback where 
> CUVIDEOFORMAT::min_num_decode_surfaces is reported
> +    ctx->cuparseinfo.ulMaxNumDecodeSurfaces = 1;
>       ctx->cuparseinfo.ulMaxDisplayDelay = (avctx->flags & 
> AV_CODEC_FLAG_LOW_DELAY) ? 0 : CUVID_MAX_DISPLAY_DELAY;
>       ctx->cuparseinfo.pUserData = avctx;
>       ctx->cuparseinfo.pfnSequenceCallback = cuvid_handle_video_sequence;