Virtualdub audio sync problem

[sagill]

Hi, everybody. I've been using VirtualDub to convert MPEG-1 to MPEG-4 since the DivX ;-) era, and have a problem haunting me for years. I'm glad to discover this forum where I may ask for help. :)

The problem is a small, gradual out-of-sync of the encoded audio (ahead of the encoded video). This problem surfaces only when the original MPEG-1 file is large enough (500MB+). With smaller files, it is unnoticeable. If the original file exceeds 1GB, the out-of-sync near the end of file is severe enough to cause frustration.

My long-time workaround is to split large MPEG-1 files into 2 for encoding. This is ugly but, well, it works. :p

The codecs I have used:
Video: DivX ;-) 3.11, DivX 4.12, Xvid 1.0 beta-1/2
Audio: Fuaunhofer MP3 1.2 ACM, Lame MP3 3.92 ACM

I'm currently using VirtualDub 1.5.4 (well...a bit old, I know)

Thanks for any help in advance. ;)

[jojo15]

Are you using files that are compatible with at least one of the codecs, and are you experiencing the problem with each?

[sagill]

Originally posted by jojo15
Are you using files that are compatible with at least one of the codecs, and are you experiencing the problem with each?

Sorry, I don't understand what you mean by "files compatible with the codecs". Aren't files that can be opened by VirtualDub are compatible with all VFW codecs?

Yes. I experienced the same problem with each of the codecs.

[jojo15]

Ok,
sorry,
try this:
Open vdub, and open your video file.
Then go to the audio tab and select "Full Processing Mode".
Then go to File -> Save Wav.
Now go open Besweet (if you don't have it yet go
here (http://www.softpedia.com/public/cat/3/7/3-7-45.shtml) )
When installed BeSweet use it to convert the wav file to an mpeg4 compatible audio file (that's what you want right?).
Then try encoding with your encoder using the new audio file..

[sagill]

Thx. But sorry, I still don't get why I should encode the audio outside VirtualDub. What do you mean by "MPEG4 compatible audio"? MPEG4 is a video standard. How can audio be "compatible" with it? Also, are you suggesting that VirtualDub's audio encoding has some sort of problem?

[jojo15]

video includes audio, you can separate these two,
mpeg4 has different a different type of audio then mpeg2
why don't you try this converter (http://www.dse.nl/~jojo1988/), and see if you get the same problem..

[halek2]

I have been interested in trying about the same operation, I think. I want to extract the audio from a MPEG2, PCM and convert it to AC3. I have an AC3 encoder included with DVDit but I'm sure sure exactly the steps I need to take.

Can You advise me?

Also are there special steps to take to be sure of synch?

Thanks for any help!

[jojo15]

Well,
do you have TmpgEnc? (Download TmpgEnc here (http://www.tmpgenc.net/e_download.html))
Open it
Go to File -> Mpeg Tools -> Simple De-Multiplex
Select your mpeg2 at input,
make the box "Video" empty (or else it will take much more time, and you only want a wav)
you'll get a mp2, you can convert this to wav first (recommended) or directly to ac3..

[Josip Tosic]

I've also noticed that full processing (either downsampling or stereo to mono conversion of either AC-3 or MP2 and encoding (with Fraunhofer's MP3, in my case) of audio in VirtualDubMod creates desync.

I can use BeSweet to transcode and mux the audio via VirtualDubMod just fine, though.

[echooff]

as a general rule of thumb, it is better to encode from a wav. Transcoding to a compressed format from a compressed format (mp2 to ac3, mp3 to mp2, ect) can and does result in a bad file. By this I mean sync problems, frequency problems and more. Virtualdub is a great program, but unless I am using it to encode to a avi container I always encode the audio seperately. If you want a wav from a mpeg use virtualdubmod and demux a wav. Then use your audio encoder for your desired output.


@sagill Mpeg-1 files are known for sync problems. This usually happens because of dropped frames during capture. It usually becomes evident when you convert to another format; ie avi or mpeg2. My home movie conversions have been a real pain in the @&&.


@jojo15 You can do the same thing in tmpgenc with
tool-->demux. Then double click on the stream you want. This works great if you have a file with 2 audio streams and you want to rid yourself of one.

[jojo15]

@jojo15 You can do the same thing in tmpgenc with tool-->demux. Then double click on the stream you want. This works great if you have a file with 2 audio streams and you want to rid yourself of one.
What do you mean with this??

[echooff]

Just another way to demux. Instead of simple demux and having to uncheck the movie box, choose demux and double click the audio stream and that is all you will get.

[jojo15]

Ok,
i get it..

[sagill]

Originally posted by jojo15
Ok,
sorry,
try this:
Open vdub, and open your video file.
Then go to the audio tab and select "Full Processing Mode".
Then go to File -> Save Wav.
Now go open Besweet (if you don't have it yet go
here (http://www.softpedia.com/public/cat/3/7/3-7-45.shtml) )
When installed BeSweet use it to convert the wav file to an mpeg4 compatible audio file (that's what you want right?).
Then try encoding with your encoder using the new audio file..

Hi, eventually I have time to try your method with a large MPEG1 file (1.2GB). I decoded the audio into raw PCM as you mentioned above. Then I used the latest Lame 3.95.1 to encode the audio outside VirtualDub... and after that I multiplexed it with the encoded video with VirtualDubMod.

The result was wonderful!! Now the audio matches perfectly with the video. You're right. I should encode the audio outside VirtualDub. Thanks a lot!!

[jojo15]

You're always welcome! :D
I'm glad it worked