[FFmpeg-devel] [PATCH] lavfi/vf_decimate: add mixed option to process input only partially to be decimated

[mail at nodoa.me]

The purpose of this new option is to enable processing of mixed content such
as TV recordings or even movies which have some cuts in telecined 24fps and
others in 30p.

Enabling it (mixed=1) will calculate a common timebase between decimated and
non-decimated content and set frame duration according to whether the
current cycle contains a frame deemed to be a duplicate or not.

The default is disabled (mixed=0) and keeping it disabled will keep the PTS
as before (verified using ffprobe).

 

Regarding setting frame->pts, I had to adjust this part a bit as it is no
longer possible to assume all frames counted by frame_count_in have the same
duration.

As for outlink->frame_rate, I have removed the assignment in the case of
mixed content as the output will be of variable frame rate. Please tell me
in case this is not sufficient to signalize VFR content.

 

An example for verifying the result is
http://samples.ffmpeg.org/HDTV/Hellboy.ts

ffmpeg -i Hellboy.ts -map 0:v -c:v libx264 -vf
fps=fps=30000/1001,fieldmatch,decimate=mixed=1,fps=fps=120000/1001 -preset
veryfast -crf 10 Hellboy.mp4

The source has a frame rate of 30000/1001 -> timebase 1001/30000 which with
a decimation cycle of 5 results in a decimated timebase of 24000/1001 and a
common timebase of 1001/120000.

The source contains 24fps interlaced content which will result in a duration
of 5 frames at the output frame rate of 120000/1001.

The source also contains 30p content which in the output will have a
duration of 4 frames.

This particular source requires the frame rate to be set to constant
30000/1001. I haven't looked into why but I have verified this to also be
required if not applying this patch.