w3fdif inserting extraneous frame (at beginning?) when selective deinterlacing all-progressive input

[Tim]

ffmpeg -i sample.mkv -vcodec prores -vf yadif=deint=interlaced -y yadif.mkv

frame=   34 fps=0.0 q=-0.0 Lsize=     144kB time=00:00:01.38 bitrate= 850.5kbits/s speed=31.6x

ffmpeg -i sample.mkv -vcodec prores -vf w3fdif=deint=interlaced -y w3fdif.mkv

frame=   35 fps=0.0 q=-0.0 Lsize=     148kB time=00:00:01.38 bitrate= 875.4kbits/s speed=33.3x

mkvinfo -v w3fdif.mkv | grep timestamp

| + Cluster timestamp: 00:00:00.000000000
| + Simple block: key, track number 1, 1 frame(s), timestamp 00:00:00.000000000
| + Cluster timestamp: 00:00:00.017000000
| + Simple block: key, track number 1, 1 frame(s), timestamp 00:00:00.017000000 <-- extra frame here???
| + Cluster timestamp: 00:00:00.050000000
| + Simple block: key, track number 1, 1 frame(s), timestamp 00:00:00.050000000

mkvinfo -v yadif.mkv | grep timestamp

| + Cluster timestamp: 00:00:00.000000000
| + Simple block: key, track number 1, 1 frame(s), timestamp 00:00:00.000000000
| + Cluster timestamp: 00:00:00.050000000
| + Simple block: key, track number 1, 1 frame(s), timestamp 00:00:00.050000000

[Tim]

All-progressive sample

[Tim]

Looking at yadif_common.c and checking for behavior differences, I notice ff_yadif_filter_frame() returns before the call to ff_filter_frame() when !yadif->prev, whereas filter_frame() checks for !s->prev but later (so in case of selective deinterlacing, ff_filter_frame() is called even when !s->prev)…

I guess the following might be a possible solution, but this is pure guesswork:

diff --git a/libavfilter/vf_w3fdif.c b/libavfilter/vf_w3fdif.c
index c2ea76dfa3..41a45ea06c 100644
--- a/libavfilter/vf_w3fdif.c
+++ b/libavfilter/vf_w3fdif.c
@@ -526,6 +526,9 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *frame)
             return AVERROR(ENOMEM);
     }
 
+    if (!s->prev)
+        return 0;
+
     if ((s->deint && !s->cur->interlaced_frame) || ctx->is_disabled) {
         AVFrame *out = av_frame_clone(s->cur);
         if (!out)
@@ -537,9 +540,6 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *frame)
         return ff_filter_frame(ctx->outputs[0], out);
     }
 
-    if (!s->prev)
-        return 0;
-
     ret = filter(ctx, 0);
     if (ret < 0 || s->mode == 0)
         return ret;

[Elon Musk]

Fixed in bbbf95848b3480ca7b8d2ede51c338cde7cb7ced