Sound in sync in mpg but out of sync after demultiplex

[falco533]

I have a Happauge Digital TV capture card, and most of my recordings that I convert to DVD I have no problems.
But recently I am having problems with (presumably) dropped frames.
The card captures to a mpg file. When I play the mpg file the audio is in sync, but once I demultiplex the files for authoring; the sound is sometimes 5-10 seconds out.
Can anybody tell me if this can be fixed, and secondly why is the mpg file audio in sync but not the demultiplexed ac3 and the m2v files

[yoda313]

Hello,

Why are you demultiplexing it???? Whats your destination???

If your making it into a DVD just leave the mpg file as it is. Or is this for editing???? I wouldn't touch it if your making a dvd.....

Kevin

[ChrissyBoy]

and secondly why is the mpg file audio in sync but not the demultiplexed ac3 and the m2v files

This is because the ac3 and m2v elementary streams do not contain timing information. The mpg file (program stream) does. I.e. the program stream has presentation timestamps for the audio and video which tell the decoder (software player or DVD player) when to present/play each stream packet. When you demux you lose this timing info. Thus when you combine the elementary streams again the new timing is calculated and may not be true to the original, if frames are dropped.

So the question is what authoring software are you using? You would most likely be better off with one that accepted program streams instead or elementary streams.

[falco533]

Thanks for the replies.
I am using DVD Lab Pro for Authoring, and it automatically demultiplex it.
Are you saying if I use a authoring program that doesnt demultiplex the sound will be in sync.

[ChrissyBoy]

Well there is a higher chance that sync will be maintained. Try the SVCD2DVD v2 demo - it doesn't demux. Let us know if your sync is maintained.

[falco]

With the SVCD2DVD program it appears that the sync is maintained, BUT it has HUGE amounts of pixellation. It obviously doesnt like the source digital tv stream.
Its a shame as it looks like quite a nifty little program.
Any other suggestions.
I have tried TMPGenc Author
Ulead DVD workshop
DVD Lab PRO
They all demultiplex it.

[ChrissyBoy]

What are the properties of the source?

[Nelson37]

Try this.

Open the file in TMPGenc Demux. See if there is a Padding Stream. Demux this stream, see if size is greater than 1k.

I do not know what the padding stream is or contains, other than it is present in many capture files and is somehow used to supply corrective synch info, even when there are no dropped frames reported. What I do know is that anytime the padding stream is larger than 1k, demux/remux will result in loss of synch. I believe it has more do with broken GOP's as it seems to be more evident in capped TV programs which contain commercial breaks, as opposed to continuous movie caps.

You must demux/remux using a prog which utilizes this padding stream for correction, while still eliminating it.

M2EditPro, MpegVCR, and TMPGenc Merge and Cut function all apparently do this. I have had best success with TMPGenc.

[spiderman2k1]

I have had a problem like this before on my Dazzle 2. Use TMPG or MPEG2VCR demultiplex put it back together and seeif that fixes the problem. If that does not work use TMPG to encode the hole file Video and Audio at the same time. This should fix the problem.

MPEG2VCR you canfix the audio by hand but its a big pain in the ass to fix it.

[falco]

I cant use TMPGenc to fix it as its AC3 audio.

[Nelson37]

I know TMPGenc will Mux an AC3 file, I do it all the time. Not sure if Merge and Cut will handle it. But you CAN check for that padding stream.