MakeMKV changes frame rate?

[chris429]

Hi all,

I have been using MakeMKV to remux a DVD with multiple VOB to individual episodes. When I ran the VOB and the remux through VLC I noticed that the remux had an extra 1-2 seconds on average of runtime. Checking the files with MediaInfo revealed that the VOB files have a frame rate of 24000/1001 while the remux have a frame rate of 23976/1000. Any idea what's going on?

Thanks!

[hardy]

means nothing, literally

MediaInfo example
Frame rate : 23.976 (24000/1001) FPS
Original frame rate : 23.976 (23976/1000) FPS

It doesn't change anything.

[hardy]

Trust me, you have nothing to worry about.

[chris429]

Thanks for the reply, hardy. Your post is reassuring.

However, I am a little concerned my files are having their run time increased, even if by a mere 2 seconds. Surely this shouldn't be happening? I haven't actually watched a full episode but the audio still seems to be in sync. It's worth mentioning that this throws the seek time off by 2-10 seconds compared to the original VOB. For example, time 2:36 in the VOB will correspond to time 2:46 in the remux, or something similar.

This also doesn't happen on all files. I remux'd a different DVD today that was interlaced and both the VOB and the remux have a frame rate of 30000/1001.

[jagabo]

The difference between 24000/1001 and 23976/1000 is one part in a million. Your movie would have to be 1 million seconds long for there to be a difference of 1 second. That's about 278 hours. Or, at the end of a 3 hour movie the time will be off by ~10 milliseconds, ~1/4 of a frame.

[chris429]

Yeah, I've done the math and I realize it's a very minor difference, but why should there be a difference in the frame rate at all? Also, why are my remux files approximately 2 seconds longer and what's going on with the seek time being 2-10 seconds off? I can only assume that's because of the different in frame rate...

I'm sorry, not trying to be difficult, just trying to learn about this stuff.

Thank you!

[jagabo]

Yeah, I've done the math and I realize it's a very minor difference, but why should there be a difference in the frame rate at all?

You'll have to ask the author of MakeMKV and/or MediaInfo.

Also, why are my remux files approximately 2 seconds longer

This could be as simple as the audio track being longer than the video track (or vice versa), or the audio track being skewed from the video track (ie, starting 2 seconds later or earlier), and MediaInfo is reporting the running times differently.

and what's going on with the seek time being 2-10 seconds off?

This could be a matter of keyframes and whether the player is seeking to the nearest keyframe ("fast seeking") rather than the actual time you requested. This should only be a matter of about 1/2 second with DVD sources (but is often as much as 10 seconds with h.264 video).

I don't know how well MakeMKV deals with variable frame rate DVDs. NTSC DVD always outputs 60000/1001 fields per second after pulldown (if any) is applied. But the VOB file may contain anywhere from 19.98 fps to 29.97 fps progressive frames with pulldown flags, changing at any time. I sometimes see DVDs where a few seconds of black at the start is encoded as 29.97i but the rest is 23.976p with pulldown flags. Or the studio logo at the start is different from the body of the movie. Things like this confuse many programs. I don't know about MKV. But, as others have pointed out, if you don't have any A/V sync problems when playing the files I wouldn't worry about it.

[chris429]

The video file is 2 seconds longer in VLC/MPC-HC, not MediaInfo. It does seem like it's nothing to worry about though because I don't notice any A/V sync issues. Thanks for the help.

[manono]

One uses drop frame timing to compute the length, the other doesn't. If you were to figure the length based on 23.976fps (the MKV) and again at 24fps (the DVD), the difference will be your 2 seconds.

[chris429]

What is drop frame timing? Is the change anything to worry about? Is there any way to avoid MakeMKV from changing to drop frame timing and just use the original frame rate of 24fps??

Thanks

[manono]

What is drop frame timing?

You could easily look it up. For example:

https://documentation.apple.com/en/finalcutpro/usermanual/index.html#chapter=D%26secti...6%26tasks=true

DVD players usually show the times based on 30fps (or 24fps, if you prefer). Your MKV shows it based on 29.97fps (or 23.976fps, if you prefer).

Is the change anything to worry about?

As already mentioned a couple of times, no.

Is there any way to avoid MakeMKV from changing to drop frame timing and just use the original frame rate of 24fps??

Why? It makes no difference. The video length is the same, no matter which convention you're using. I do all my work in 23.976fps so I'd rather the DVD player reflect that, rather than having MakeMKV create 24fps videos.

[hardy]

like i said, changes nothing
topic should be closed