AVI to mpeg2 - audio out of sync

[flumpf]

I have some pal avi files I want to convert to mpeg2. I downloaded and installed the k-lite mega pack from free-codecs.com. Using several different encoders, the audio is out of sync every time. I am not converting from pal to ntsc. Any ideas why this is happening?

[steveryan]

Codec packs are bad news. Load your files into the latest Gspot and that will tell you which codecs you require. I'd guess that MP3 VBR is causing the problem, read this - https://forum.videohelp.com/viewtopic.php?t=309224

[flumpf]

Well Gspot does report that the audio is vbr mp3. I followed the instructions in the thread you linked to, but the new avi that virtualdubmod creates has the same audio sync problem again...?

[redwudz]

Is the sync error the same throughout the video or does it gradually drift out of sync as it plays? The first can be fixed by offsetting the audio from the video. VirtualDub can do that. The second is what you often get with VBR audio when encoding to MPEG. It can also be caused by the audio and video files being different lengths. If so, one needs adjusting.

The original AVI file with VBR audio should play fine and in sync if it's not corrupted. It's mainly when you try to encode to MPEG when the VBR causes problems. Most likely because the encoder can't 'read' the length of the VBR audio and gets it wrong. Changing it to CBR or a WAV format fixes that. If you have done that properly, you likely have a file with corrupted frames or other problems.

[flumpf]

I've done some further experimenting with these files. They are xvid 1.0.2 avi's with vbr mp3 audio. I see no evidence of corruption or lost frames. I've processed 3 files according to instructions at https://forum.videohelp.com/viewtopic.php?t=309224

2 of the 3 continued to have sync problems. The other one had the sync issue go away. I notice the audio track for the 2 with problems is about 4-5 seconds shorter in length than the video track. This being the case, how can I fix the problem with these files? Thanks

[redwudz]

If you save out the audio as a WAV (Full processing) with VirtualDub Mod, then 'Import' it into Audacity, then 'Edit>Select All', then in 'Effect>Change tempo' and you can adjust the length the same as the video.

If you have to make major adjustments, or the video is very short, you may also have to adjust the pitch to make it sound right. Then save out again as a WAV or a MP3 using the Lame MP3 codec with Audacity.

Then you can add it back with the video in VDM to check the sync. Or you can use the modified WAV and convert it to AC3 with ffmpeggui and use that for your DVD audio.

[flumpf]

How do I adjust the audio using virtualdubmod? Would rather not have to bring another program into this. I see in one of the guides an audio skew correction setting under Audio/Video Interleave Options but can't figure out how to get to this.

And btw, why is there a virtualdub and a virtualdubmod?

[redwudz]

VD Mod can open MPEG, OGM and some other formats that VD can't see. I also like how it handles the audio compared to VD. There are several other 'flavors' of VD also.

To get to 'Audio Skew' you have to activate full audio processing in VDM, then select 'Interleaving' and you will see the 'Audio skew correction' window. The time is in milliseconds. (Thousands of a second) One second equals 1000 milliseconds. You can use a + or - correction. The difficulty is finding the exact correction. Some use MPlayer or similar and move the offset in there to determine the offset value. Then you save out the file with the proper offset. I have to admit, I haven't had a lot of luck with this method, but it works for others.