Guide: Having gradual sync problems after MPEG1 encode?

[calamari]

This should allow you to fix gradual sync problems that occur after an AVI is encoded to MPEG1/2. If the sync problems happen right away, then this procedure probably won't fix them. Also, if the audio/video are different lengths because the AVI is broken at the end, this also won't fix it. I am working on a tool to repair the end of a broken AVI.

Tools required:
VirtualDub
AVIFix

1. Open the AVI in VirtualDub.

2. Save the audio portion as a WAV. If the audio is compressed, you'll want to go to the Audio menu, choose Full Processing mode, and change the Audio settings to be uncompressed PCM, then save as WAV:



3. Close VirtualDub.

4. Run AVIFix and open your AVI and WAV files.

5. Write down the original AVI information:



6. Click "Sync A/V" to match the video to the audio length.

7. Save the changes to the AVI.

8. Convert the modified AVI to MPEG, using the saved WAV from Step 2 for audio.

Now the audio and video should be syncronized.

calamari

[calamari]

Just wanted to update everyone interested on the status of this program. From everything I can tell it should be working fine. However there are some situations where it may not be able to help (yet!):

1) If the audio starts late or early -- this one is obvious because the sync problems happen right away.. use the existing methods on vcdhelp.com to fix this.

2) If the audio ends late or early because of a file error -- this one I ran into and it wasn't easy for me to tell. The problem came from a corrupted AVI that someone had clipped at 700MB so it would fit on a CD-R.

What I'm working on is a tool that will allow for clipping off the last frame of audio & video. Then, if there was an AVI error or weird cutoff of audio or video it will be fixed and AviFix will be able to do its job to fix your AVI

calamari

[calamari]

The Windows version of AVIFix is ready.

Have fun,
calamari

[calamari]

AVIFix 1.20 is out. New features:
* No longer requires COMDLG32.OCX
* Remembers last directory for AVI and WAV files

calamari

[Daagar]

I'm anxious to try this program out. I use the standard convert AVI to WAV in full processing mode in VDub, than TMPGEnc everything, which for the most part works. However, it is very common that the audio will get ever so slightly out-of-sync at times during the film. It usually isn't drastic, and is more noticable in high-action or rapid-talking scenes.

One quirk... your guide above says to write down all those numbers, but then never indicates what to do with them... I haven't tried the program yet, so this may be more obvious once I do.

[homerpez]

Is this AVI as in AVI, or AVI as in DivX?

I've never once had a synch problem with an AVI I've captured (Huffy), but I have problems all the time with DivX's. Not to mention "decode" errors in video streams with DivX...

[calamari]

Daagar:

Sorry for the confusion! Writing down the numbers is just in case something goes wrong and you want to revert back to the original. Just type them back in the same boxes they came from and save the AVI, and you're back to the original file.

homerpez:

It should work on any kind of AVI, but make sure you extract the audio as an uncompressed WAV. I'm seeing where it might be best to extract in Full processing mode rather than Direct stream copy, but try either way.. it might make a difference depending on the way the AVI is messed up.

Let me know how it goes,
calamari

[Daagar]

Another question. When looking at the File->File Information in VirtualDub, there is a 'preload skew' box, which usually has a number varying from 0.01s up to as large as 0.58s (that I've seen). Does this have any bearing on audio sync when going from avi(divx) to mpeg-1?

[calamari]

Not sure.. haven't messed with that option at all. If you want to do some experiments I'd be interested to know if the option makes a difference when a WAV is used for the audio part of the encoding.

calamari

[Daagar]

Finally had a chance to do a conversion using AVIFix. The results are _very_ promising.

Source: 640x272 DivX AVI, 5Ch. audio

Steps:
1. Let TMPGEnc do the audio conversion first (File->Output to File WAV). The gave me the uncompressed WAV (VirtualDub had trouble with it).

2. Loaded the original .avi and the .wav into AVIFix and resync'd the A/V.

3. Used TMPGEnc (via the External Tools) to convert the .WAV to a 44.1KHz mp2 file (via SSRC and tooLAME).

4. Used FitCD to create an AviSynth file with a 704x480 destination (I use Kwag's KVCDx2 template).

5. Loaded the .avs file from step 2 into TMPGEnc and did the video conversion.

6. Used File->MPEG Tools in TMPGEnc to multiplex the converted movie file with the .mp2 file created in step 3.

7. Played the file back in WinDVD. Scanned to various parts and was unable to detect ANY desync at all.

If it plays just as well in my standalone DVD player, I'll be thrilled. Thanks a ton, calamari.