#233 Out of sync issues after reencoding

[Anonymous]

Hi Anton,

as always many, many thanks for your work! Virtualdub2 is an awesome tool!

Just a few days ago I started to have out of sync problems that I did not have before at all.

Let me explain:
I do screen captures using Nvidia Shadowplay (not using Virtualdub2) and get a huge h264 file which is IN-SYNC. In the Nvidia driver settings I request 30fps. I load this captured mkv file into Virtualdub2, edit start and end, then recompress audio to CBR 192k MP3 and video to x264 CRF=18 main profile level 4.1 and save it again as mkv.

That worked perfectly for about 1 year.

I recently had to update Nvidia drivers, so it might be that this update changed something to the captured videostreams. Still the originally captured file is IN-SYNC, only after reencoding I get progressively out-of-sync issues. Out of sync becomes really bad after 1h or so in the file.

So far, I scanned the video stream for errors (none found) and I also encoded with Megui (same settings) which also gives an out-of-sync file. I also tried the most recent Virtualdub2 version which gave me the same result.

I'm pretty much out of ideas now what could be the problem - any idea from your side would be greatly appreciated!!

All the best, Hannes

[Anton Shekhovtsov]

Thanks,
This is probably related to variable frame rate. Unfortunately this feature is currently not supported in vd2.

[Anton Shekhovtsov]

Did you mean the file is perfectly in sync when viewing in a player? Not within vd2?

[Anonymous]

Yes, I use vlc to check the audio sync (not vd2).

What do you mean variable frame rate is not supported by vd2? As vd2 is also used for capturing, I thought that it naturally supports variable frame rate for encodings?

Or do you mean vd2 does not support variable frame rate for playback only?

[Anton Shekhovtsov]

There is one form of VFR that works: null frames in AVI. This is what appers as inserted frames in capture / dropped frames in playback. Should work with internal AVI driver.
What is the file format from shadowplay? I assumed it is mp4. If you open mp4 in vd2, by default it uses "caching input driver". This is where VFR support is poor/missing.

[Anonymous]

What is the file format from shadowplay? I assumed it is mp4.

That's correct, but I use mkvtoolnix to combine the file segments into one file and mux to mkv before further processing.

Is it the same issue for mkv's?

[Anton Shekhovtsov]

Same.

[Anonymous]

So I guess when vd2 can't do it and also avisynth can't do it, I need to use some entirely new tool like handbrake?

Or there any other options?

Many thanks for your great input!!

[Anton Shekhovtsov]

I can't really answer this. There should be many programs that can reencode and preserve original timestamps (can you use bare ffmpeg?)