[vlc-devel] [PATCH] transcode: video: fix filter drain

[Alexandre Janniaux]

Hi,

Note that the whole filtering pipeline could be improved by
forcing filter_chain_VideoFilter to always return either
zero or one picture, or at least for filters using GPU
resources, and allow to drain as many time as there is an
output picture.

It would allow better control over the back pressure, in
particular if filters are drained from the last one first
instead of the first one.

The issue is different in the video output pipeline, which
doesn't seem to support this at all.

Somehow refers #12155 although it is not the main topic of
the ticket.

Regards,
--
Alexandre Janniaux
Videolabs

On Mon, Jul 20, 2020 at 05:57:27PM +0200, Alexandre Janniaux wrote:
> When filters like deinterlace are returning multiple pictures, forcing
> the filtering of the second picture in a filter chain can be done by
> calling filter_chain_VideoFilter with NULL.
>
> Without this, additional pictures are dropped instead of being filtered
> and encoded.
> ---
>  modules/stream_out/transcode/video.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/modules/stream_out/transcode/video.c b/modules/stream_out/transcode/video.c
> index 23fa505e358..f0214d16645 100644
> --- a/modules/stream_out/transcode/video.c
> +++ b/modules/stream_out/transcode/video.c
> @@ -663,7 +663,7 @@ int transcode_video_process( sout_stream_t *p_stream, sout_stream_id_sys_t *id,
>              filter_chain_t * primary_chains[] = { id->p_f_chain,
>                                                    id->p_conv_nonstatic,
>                                                    id->p_conv_static };
> -            for( size_t i=0; p_in && i<ARRAY_SIZE(primary_chains); i++ )
> +            for( size_t i=0; i<ARRAY_SIZE(primary_chains); i++ )
>              {
>                  if( !primary_chains[i] )
>                      continue;
> --
> 2.27.0
>