MKV [h264/aac] to mp4 conversion problems...

[DestructoEH]

I've never really understood encoding/muxing, so I decided to learn by undertaking a small job for myself. I'm converting an anime series from mkv to mp4 (for streaming playback on my Xbox360).

The first two episodes have gone perfectly, audio/video in sync, hardcoded subs... absolutely perfect. Well to my suprise, when I get to episode 3 I'm having a/v sync issues. Already retraced my steps and checked everything, I've done nothing different in my process with this file:

use MKVextractGUI to extract subs
use GOTSent to convert to MP4 (without subs)
use XviD4PSP to hardcode the subs to the finished mp4.

So far, so good... until now. FPS stated as 29.970, ends up being too fast. Tried reencoding at 25 fps, works great at the beginning, but ends up out of sync a bit later on. I'm assuming this episode has variable fps, and I can't figure out how to create a good median for it. I'm using AlltoAVI now to see how it works, but the job isn't finished yet, so I can't comment on it. GSpot would not show me any info in the mkv container, but it would play the file.

For the record, files are mkv wrapper/h.264/aac audio, all 13 episodes released from the same group in the same format.

Can anyone give me some ideas on what to do?

[jagabo]

Try 23.976 fps.

[FulciLives]

I believe that XVID4PSP can open MKV files. If you are using it to re-encode and the AAC audio in the original is 2.0 (meaning no re-encode should be done) then you should be using XVID4PSP directly.

The only time XVID4PSP would choke is if the AAC input is something other than 2.0 (like 5.1) and you want to re-encode it.

For some reason XVID4PSP can't handle 5.1 AAC input unless I think you are just passing it through but that's no good as the XboX 360 does not support 5.1 AAC audio.

- John "FulciLives" Coleman

[FulciLives]

Try 23.976 fps.

Most anime in a MKV would be 23.976fps

So this is a good suggestion.

- John "FulciLives" Coleman

[DestructoEH]

Thanks for the suggestions, I'll definitely try 23.976 fps. Like I said, this is the only episode I've had a sync issue with. The audio is 2 channel aac. It probably is overkill to use GOTSent first, but the last time I tried to just encode the MKV directly through XviD4PSP it crashed.

MediaInfo states the audio is about 2.00190 seconds longer than the video. I suppose the variable framerate makes up for this length difference? I'll try some of your suggestions and get back to you.

Thanks.

[DestructoEH]

23.976 did the trick, it's perfectly in sync now. Thank you.

I did notice that fast action scenes are a bit choppy now, that's to be expected I suppose. In XviD4PSP's video options, you can set which framerate converter to use. I used the ChangeFPS option (which deletes or duplicates frames), would any of the other options (AssumeFPS, ConvertFPS, or MSUFrameRate) do a better job with the choppiness? Or is this just going to be unavoidable?

[jagabo]

You shouldn't bother changing the frame rate at all. If you were making DVDs you would leave it at 23.976 and use 3:2 pulldown flags. The only way you can reduce the choppiness (and keep the running time) is to use a motion vector based frame interplator like AviSynth's SmoothFPS(). That usually generates some motion artifacts too though.

https://forum.videohelp.com/topic303037.html#1533994