Re: [FFmpeg-devel] [PATCH] lavfi/vf_fieldmatch: keep fields as-is if not matched properly

[Paul B Mahol <onemda@gmail.com>]

On 11/3/22, mail@nodoa.me <mail@nodoa.me> wrote:
> Makes it possible to use deinterlacers which output one frame for each field
> as fallback if field
> matching fails (combmatch=full).
>
> Currently, the documented example with fallback on a post-deinterlacer will
> only work in case the
> deinterlacer outputs one frame per first field (as yadif=mode=0). The reason
> for that is that
> fieldmatch will attempt to match the second field regardless of whether it
> recognizes the end
> result is still interlaced. This produces garbled output with for example
> mixed telecined 24fps and
> 60i content combined with a field-based deinterlaced such as yadif=mode=1.
> This patch orders fieldmatch to revert to using the second field of the
> current frame in case the
> end result is still interlaced and a post-deinterlacer is assumed to be
> used.
>

Are there samples, ways to reproduce this?

> Signed-off-by: lovesyk <lovesyk@users.noreply.github.com>
> ---
>  libavfilter/vf_fieldmatch.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/libavfilter/vf_fieldmatch.c b/libavfilter/vf_fieldmatch.c
> index 40e559df9e..bf946beec9 100644
> --- a/libavfilter/vf_fieldmatch.c
> +++ b/libavfilter/vf_fieldmatch.c
> @@ -680,7 +680,7 @@ static int filter_frame(AVFilterLink *inlink, AVFrame
> *in)
>      AVFilterLink *outlink = ctx->outputs[0];
>      FieldMatchContext *fm = ctx->priv;
>      int combs[] = { -1, -1, -1, -1, -1 };
> -    int order, field, i, match, sc = 0, ret = 0;
> +    int order, field, i, match, interlaced_frame, sc = 0, ret = 0;
>      const int *fxo;
>      AVFrame *gen_frames[] = { NULL, NULL, NULL, NULL, NULL };
>      AVFrame *dst = NULL;
> @@ -793,6 +793,12 @@ static int filter_frame(AVFilterLink *inlink, AVFrame
> *in)
>          }
>      }
>
> +    /* keep fields as-is if not matched properly */
> +    interlaced_frame = combs[match] >= fm->combpel;
> +    if (interlaced_frame && fm->combmatch == COMBMATCH_FULL) {
> +        match = mC;
> +    }
> +
>      /* get output frame and drop the others */
>      if (fm->ppsrc) {
>          /* field matching was based on a filtered/post-processed input, we
> now
> @@ -813,7 +819,7 @@ static int filter_frame(AVFilterLink *inlink, AVFrame
> *in)
>
>      /* mark the frame we are unable to match properly as interlaced so a
> proper
>       * de-interlacer can take the relay */
> -    dst->interlaced_frame = combs[match] >= fm->combpel;
> +    dst->interlaced_frame = interlaced_frame;
>      if (dst->interlaced_frame) {
>          av_log(ctx, AV_LOG_WARNING, "Frame #%"PRId64" at %s is still
> interlaced\n",
>                 outlink->frame_count_in, av_ts2timestr(in->pts,
> &inlink->time_base));
> --
> 2.34.2
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