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Old 2nd June 2018, 10:44   #1  |  Link
fireattack
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Join Date: Nov 2017
Posts: 9
NTSC film (23.976 progrressive soft-telecine) DVD playback FPS and remux problem

Hi everyone,

Recently I was encoding an NTSC DVD that has actual content of 100% FILM (23.976p, with pulldown tag for soft telecine). After playing with it for a while, I have two questions which I can't find answer anywhere.

1. why is this film DVD played back in 24 fps instead of 23.976 fps on computer?

When playing back this DVD directly on a computer, it is expected to play as-is instead of trying to soft-telecine it, since it's unnecessary. The actual FPS is indeed ~24 when playing. However, with *all* the players I tried, including VLC, MPC-hc, MPC-be, MPV, etc., I noticed that it is played back in 24fps, instead of 23.976fps, despite that's what it says in the meta tag (24000/1001).

I know it not because I can tell such small difference, but because the duration of the video is shown ~1:25:21. While if I encode it, or even just remux it with MakeMKV, it will be ~1:25:26. The difference of these two duration is exactly 1000/1001. You can also see this difference if you only play just one .vob file (vs. encoded version) as well, albeit the difference will be very small (<1s) for shorter videos.

On a side note, the audio file extracted by DGIndex is also ~1:25:26 (consistent with 23.976 duration). There is no audio desync either way when playing back, though.

2. why does remuxed video have inconsistent frame intervals?

I also remuxed the DVD using both MakeMKV and mkvtoolnix to a single MKV file. I then extracted its timecodes_v2 using mkvextract. The average FPS, is indeed 23.976. However I found another problem, the timecode interval is like this:

timecode Interval
0 33
33 50
83 34
117 50
167 33
200 50
250 34
284 50
334 33
367 50
417 33
450 51
501 33
534 50
584 33
617 50
667 34
701 50
751 33
784 50
834 34

...

As you can see, while the average interval is indeed ~41.71ms (1000/23.976), they're not evenly distributed, but have a 33/50/34/50 pattern. This doesn't happen in the encoded video (which would just be consistent 40/41).

So my question is:

1. why is it like this?
2. will it affect the playback? I can't tell from my eyes, but I assume having such weird interval will cause some abnormality in theory?


Thanks for your time.

Last edited by fireattack; 2nd June 2018 at 10:47. Reason: Typo
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mkv, soft-telecine

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