Audio Out-of-Sync Slowly When Encoding Using Mainconcept Encoder

[siaush]

I tried to encode a progressive scan NTSC 29.97 fps DivX AVI into DVD format using Mainconcept MPEG Encoder. My television display pictures in interlaced mode, I encoded the video in interlaced mode, top fields first. After the encoding process, I found that the audio went out of sync slowly throughout the video, it was sync-ed at the beginning part of the video but eventually went out of sync. Is there anything I can do to fix this problem?

Thank you.

[guns1inger]

Check with avicodec or g-spot to see if the audio is VBR MP3. If so, follow the instructions in this post : https://forum.videohelp.com/viewtopic.php?t=309224 up until you have the uncompressed wav version of the audio on your HDD. From there you can encode the audio separately using something like ffmpeggui, and then add it back during authoring.

[siaush]

The audio is 48Khz CBR 128kbps MP3 stream.

[guns1inger]

The other usual cause of gradual sync disparity is a change of framerate.

Open the encoded mpeg in virtualdubmpeg2 and click on File -> File Information. Make sure the video and audio lengths match. Also, compare the audio and video lengths of the mpeg with those of the original avi file.

[siaush]

Ok I'll try and post the results here, by the way, I think the problem might be caused by interlacing the video. The total frame count changed from 84,203 to 85,382 according to G-Spot.

[guns1inger]

Interlacing should not have changed the frame count, but it should have doubled the field count. If you interlace progressive video, all you really do is split the frame into two fields. The frame count should remain constant. That it has changed is a)probably the cause of your sync problem, and b) a sign that the encoding didn't work at all as planned.

[siaush]

I used the Mainconcept Encoder built in feature to interlace the videos, is there anything I can do to make it working? and in VirtualDub, it displays the correct frame count (means the output is same with the input, I don't know why).

I did try something else too, I demuxed the video to it's elementary streams. From the MPEG Video ES, G-Spot shows that the video frame count is exactly the same with the original video. But if I analyze the program stream of the MPEG file, then the frame count will be different, like I stated above.


Thanks.

[guns1inger]

Using the elementary streams, open the video track with Media Player Classic, then open the audio stream as the dub and see if they play in sync. You may be luck and just have a muxing issue, in which case remuxing or authoring with the streams may solve the problem.

[siaush]

Hrm.. It does not sync. Anyway, I make the elementary streams using TMPGEnC, not using Mainconcept MPEG Encoder.

[guns1inger]

So are they the same length (video and audio) and is the audio track the same as the original ?

Second question : are you sure the file drifts out of sync ? Sometimes is can be difficult to tell if it is out the same the whole way, or drifting out over time.

[siaush]

It's drifting out over time, I'm sure about that. Anyway, this is what I tried while waiting for your reply.

I used the elementary video stream that I made from TMPGEnc MPEG Tools, and I load the original AVI file into VirtualDUB-MPEG2 and save the audio track as mp3 file. After that I used MPC and played the elementary video file with the mp3 file extracted using VirtualDUB and surprisingly it worked well. The video and audio synced from the begining till the end. So, any idea what's wrong?

Thank you ^^.

[siaush]

Could this be the problem? Both programs are loaded with the original AVI file, Mainconcept Encoder shows a lot more of audio samples than Virtualdub do, could that be the problem that leads to the unsynced A/V ?

[guns1inger]

Use ffmpeggui to convert the mp3 file to AC3 and test again. If this still works (i.e. keeps sync) then the problem is with how mainconcept is encoding the audio.

FWIW - I never let my video encoder encode my audio.

[siaush]

I've rip the mp3 track from the original AVI file and convert it to AC3 using DVDLabs and it worked like a charm.
Anyway, is there any difference in terms of quality between the ffmpeggui AC3 encoder and DVDLabs encoder (It's using TMPGEnc AC3 Plugin)?