Audio sync problems, revisited

[cipherscribe]

Hi,

I have read a number of the posts on the forums here, trying to find an answer to my specific problem. It seems alot of ppl are having audio sync problems. Here is my speicifc problem, and if somebody has already solved it previously, please let me know!

I am trying to copy Survivior Divx avi's to vcd/svcd. I have used a number of processes, and each time the audio appears to be in sync, but then after 5-10mins starts on a never ending deviation from the video.

I recently copied a movie using the same process, and this worked fine.

I have checked the survivor avi's, and they have no sync problems. It's only with the conversion to mpg that it starts to go haywire.

What I have tried:

Copy the whole shebang using tmpgenc or;
Use virutal dub to extract the wav, then use this as the source of the sound in tmpgenc or;
Import the avi into Ulead Video Studio, and create a VCD from there;

All the time I make sure I am copying to a format that is the same FPS.

I use Nero to copy to CD, but that aint the problem, when I view the mpg prior to starting Nero,the video is already out.

Virtual dub does not complain about any errors when I scan for errors.

Can someone help me out here, this stuff is causing me headaches!

[Craig Tucker]

Might seem like an obvious question but are you using full processing mode when saving the wav file.

Craig

[DJRumpy]

Also check the TOOLS section, the doom9 site, and the www.divx.com site. There are tools to correct DIVX audio sync problems. The audio itself can be a little corrupt. When the audio is demuxed, and re-encoded into an MPEG, the problem appears.

[cipherscribe]

Thanks guys,

I shall try out the tools on doom9 and let you know how it goes,
oh, and yes, I was in full processing mode...

Thanks again.

[cipherscribe]

I couldn't find any specific apps on doom9 or divx.com that relate to fixing audio issues.

Can you be more specific?

My primary problem is not that the audio is out of sync within the .avi, it's perfect there, it's only after the tmpgenc conversion....

)-:

[DJRumpy]

What is the framerate of your source, and what options did you use in TMPGenc when encoding (specifically, under the Advanced section).

Also, let me know what type of audio format your DIVX has. Depending on the type, there are a couple of different ways to tackle the problem.

If your DIVX audio is AC3, look for AC3Fix. Corrupt frames will cause audio sync problems when it's converted to MPG. When you save an AC3 from VirtualDub this way, it introduces this problem. Use AC3Fix to correct it, and your sync problem should clear up.

http://www.doom9.org/Soft21/Editing/DivFix1091.zip
(note, the above link is not the same app as AC3Fix. It's just another repair tool)
If the above link doesn't work, go to the doom site, then downloads, and then click 'Show Me More' in any of the subsections. It's in the AVI section. It will repair general errors in a DIVX Video and Audio stream.

[cipherscribe]

The video is 29.970 with 77980 frames
According to Gspot, the Audio is Mp3 96kb/s CBR

File length is correct. Codec is DivX 3 Low-motion.

Tmpgenc options:

Video CD, NTSC (29.970 fps).
I do not change any source source settings.
The only change I make under advanced settingsd is I set Motion search precision to High Quality (slow).

These are the only settings I make when encoding.

Some things to consier:

The AVI source is perfect, no skew or syn loss
VirtualDub finds no errors on checking the avi
DivXFix finds no errors on the avi.

I thought about the 'audio gap correct' in the source range feature, but the sound is no permenantly skewed, it starts out ok, then gets progressivley worse until it's laughable. A whole scene (5-10 seconds) can go by without hearing the audo.

I should note that that not all episodes i have cut have done this (I don't think it's the user!), episode 4 was nearly perfect, but episodes 1, 2, 3 and 5 are all skewed.

I have tried to see what the differences are between episode 4 and the rest, and the only thing that jumped out at me was that tha average audio bitrate on episode 4 was 56kb/s instead of 96kb/s.

Your thoughts?

[cipherscribe]

OMG, my typing is atrocious!

I have also tried encoding the video only, then multiplexing, but that seems to make things worse.

I don't have enough knowledge in BeSweet to know all the optimum options for my stream...

[cipherscribe]

Also,

Under the file information in VirtualDub, there is a preload Skew of 6000 samples (0.14s).

Is this bad? Could this cause the problem?

[DJRumpy]

cipher, what about the Advanced settings. Were you using 3:2 pulldown? The problem your describing sounds like the frame rate for the audio, and the video is different. Your saying the audio gets progressively worse the farther into the movie you get? I'm guessing there are no obvious video artifacts, or audio chirping to indicate jumped/lost frames?

As for the audio, you should save it as WAV, since it's MP3, and convert it elsewhere.

Another suggestion. Check your audio's length, and your video's length. Make sure they match. If your getting a warning in virtual dub, then you should definately be extracting it seperately.

The BeSweet GUI can handle converting a movie from one fps to another. It has built in clickables for PAL to NTSC, NTSC to FILM, etc. It can probably fix your problem if that is indeed whats causing it. Check your Advanced Tab to see if your using pulldown. Also make sure your Frame Rate on the Video tab matches the framerate of your source.

[cipherscribe]

Hi there DJ,

I am not clicking any of the settings in the advanced settings. 3:2 pulldown is not checked. I thought I shouldn't be converting framerate. Is this not so? Should I use the pulldown? The framerate on the video tab matches the spec of the .avi (29.97 fps)

I just created another copy. I extracted the audio, then tmpgenc. Virtual Dub tells me the mpg is 43:21. The WAV file is 43:21.958. The original .avi is 43:21 also.

Any ideas?

[DJRumpy]

It isn't necessary to use pulldown. It sounds like you've done everything correctly. Your framerate settings are also correct. The final lengths are fine, and the .14s of skew is negligable. The kind of skew your talking about is of a much larger scale.

Try converting your WAV file (it is a PCM WAV file right?) to MP2. Use TooLame in the tools section, or the BeSweet Gui for TooLame(you will still need to download TooLame if you go the BeSweetGui route), and encode your movie in TMPGenc without audio (select Video Only..bottom right corner of main screen). This should give you an M2V file. Use the MPEG TOOLS ( FILE | MPEG TOOLS | SIMPLE MULTIPLEX ). Choose the appropriate type of MPEG from the drop down, and browse to your M2V, and M2P files. The multiplex shouldn't take more than a few minutes.

You might also reverify your M2V's length before multiplexing, with the MP2's length.

[cipherscribe]

Hi DJ,

Maybe it is just the file???

I extraceted the sound from the avi using toolame, and encoded the video with tmpgenc. Both produced a length of 42:47 (survivor 4 episode 7).

When I use simple multiplex to join, I receieved the error: "110593 s packets cause buffer underflow. The MPEG file might cause error when it played"

However the file plays ok, but it still eventually goes out by about 5 seconds.

If you can't suggest anything else, thanks for the learning curve (-:

[cipherscribe]

Hi Dj,

I seem to have fixed it.

Even though sounds forge, virtual dub, tmpgenc, the original AVI, WAV, MP2 file all have a reported length of 42:47, when I shrink the WAV by three seconds in Sound Forge, all comes together beautifully.

I have tried this on a number of the episodes, and 3 seconds has always been the magic number.

Many thanks for all of your help on this one! Now I can watch without getting a headache!!

[DJRumpy]

I'm at a loss. The reported length for the WAV should have been correct. Oh well. At least your up and working. 8)