QTGMC: Every 4th Frame wrong?

[Waver]

Hi all,
checked the forum but didn't found similar problem/solution:
After applying QTGMC to a 25fps interlaced PAL the resulting video goes 3 frame forward, and than 1 frame backward.


already tried:
-disabling QTGMC (comment out with #) the frames behave as they should
-AssumeTFF: everything wrong

AviSource("1s.avi")
AssumeBFF()
ConvertToYV12(interlaced=true)
QTGMC( Preset="Slow", Sharpness=0.4, EdiThreads=2 )

I also added a sample of the Video (1 secound).


Any Ideas?

[poisondeathray]

It's because there is a problem with the declared framerate in your video

Frame rate                               : 50.000 FPS
Original frame rate                      : 25.000 FPS

For many (all?) VFW DV decoders this will cause duplicate frames at 50 FPS, bobbed to 100 FPS with duplicates

You can use FFVideoSource. It produces the correct unique frames an at the correct 25 FPS, thus QTGMC will be correct



You can review the process of how you transferred the file, or why the framerate is incorrect in the file

[jagabo]

Fixing your capture/processing to flag the frame rate properly is best. But for video's you've already captured you can use SelectEven() or SelectOdd() to remove every other frame (the duplicates) before QTGMC(). You may to AssumeFPS() to get the right frame rate too.

[Waver]

Thanks @jagabo and @poisondeathray!

In the mean time I checked some things:

• works: SelectEven() or SelectOdd()
• works not: AssumeFPS(25)

Nevertheless, I checked the workflow:

• capturing D8 with scenalyzer (more than one time because of errors)
• convert to raw dv (needed for the next step) https://theatrecollection.blogs.bristol.ac.uk/2024/05/09/the-challenges-and-rewards-of...-minidv-tapes/
• using FFMPEG ffmpeg -i input_file -f rawvideo -c:v copy output_file.dv https://amiaopensource.github.io/ffmprovisr/index.html#rewrap-dv
• repair wrong frames with DVrescue
• convert dv back to avi via ffmpeg -i merged.dv -c copy merged-raw.avi
• encoding to h264 with QTGMC

I found out, that the error comes from the back-converting: ffmpeg -i merged.dv -c copy merged-raw.avi
That seems to be not a new problem: ffmpeg misdetecting framerate of dv https://trac.ffmpeg.org/ticket/11339

My solution (seems to work at the moment) would be forcing of 25fps when converting back: ffmpeg -i merged.dv -c copy -r 25 merged-raw.avi