How to fix sync problems when converting MPEG TV captures

[Russell_hq]

If you are getting audio sync problems (audio progressivly gets out of sync) when converting mpeg tv captures e.g.. changing audio from 44.1 to 48KHz to put on a dvd or any other process where you demux the tracks then remux then I have one solution.

The original mpeg plays fine and is in sync but when you do any editing you always seem to get sync errors, sound familliar?, this happens when you demux the tracks. If you load up the demuxed audio track in Goldweave you will see the track length, now load up the video track in Virtualdub and you will get the video track length. You will notice that the track lengths are different, usually by a few seconds. Thus all you need to do is use goldweave and change the lenght of the track. This can be done in 2 ways. First way is to load the audio track in goldweave and click on the timewarp icon (a little clock) then using the time of the video from virtualdub, write this value in the length box now let goldweave do its thing and save the new audio file. Second way to do it is look in virtualdub after loading the original mpeg and under Video->Framerate write down the 2 values "Current" and "change so video and audio durations match". Go back to goldweave and load your demuxed audio track, goto effect-> playback rate and for the new rate type the result of the following sum:

(current framerate)/(change so video and audio durations match)*(demuxed audio track sample rate; typically 44,100Hz)

eg

(29.970/30.033)*44100

Now type this new number into the playback rate.

Finally goto effect->resample and type the resample rate you want, eg 48,000Hz. Goldweave will now process the track and the new track length should match the video track length.

You now have an audio track the correct length. Just multiplex with BBMpeg and you have a new MPEG with correct sound. You might get an audio sync error (audio is out of step), this can be fixed by adjusting the start-up delay of the audio track in the program stream settings.

Hope this helps someone.

[Tommyknocker]

Very innovative. I hope I never have to use it, but if I do, I am glad it is available. Have you considered submitting it as a guide? Right now it is only a very useful post. I am going to save it as a text file, in case you decide not to submit it.

[FulciLives]

I've heard people talk about GOLDWEAVE before.
How does one get it? Is it freeware/shareware or pay or what?
Is there an official website etc.

- John "FulciLives" Coleman

[Tommyknocker]

FulciLives wrote:

How does one get it? Is it freeware/shareware or pay or what?

I think he means Gold Wave. If he did, then the answer is commercial ware. Its trial version allows 120 commands before needing a reload, the registered allows unlimited commands. There is a running toll dollar amount in the bottom right corner, to remind you how much you are mooching. See the Tools section at left.

[Russell_hq]

Yeah i mean Goldwave, dunno why i wrote gold weave, must have had it stuck in my head
Gold WAVE
http://www.goldwave.com/

I will try and write a guide for this and post it later on today.

Has anyone had a chance to try this method? I want to know if its worked for anyone else, thanks.

[videocheez]

I tried the first method that you listed first because it looks easy and doesn't involve getting the calculator out. I tried the time warp to reduce the audio by about 30secs. and gold wave crashes at the end. Perhaps 30 is to much time to compress. I tried the second method also and I didn't see any value at all in the space that says "change so video and audio durations match" . Could this be because my audio is AC3? I'm going to keep trying your method because it looks viable but so far i'm stuck because i think that vdubmod doesn't see the ac3 audio.
I think im going to mux my mv2 with the PCM wav instead of with the ac3 so that vdub mod can recognise the audio. Then once I get the wav in sync with the video, I will extract the wav and reconvert it back to ac3. Do you have any suggestions? Have you started the guide yet because these sync problems that i have been having lately have kept me stuck for about four weeks.

Thanks in advance,

VC

[Russell_hq]

make sure you have enough free hard disk space as goldwave works with uncompressed sound, so when you convert the file it makes a backup of the original so you can undo changes. Therefore you need to have enough space for the backups otherwise turn off the restore function in goldwave(have a look in the menus for this, its there somewhere).

Did you manage to uncompress the sound using virtualdub, i.e.. ac3-> wav? What are the original files that you are working with, what are you tring to do/convert? is the original file in sync? when you demux the original file are the audio and video tracks different lengths?

Try downloading nandub, i think it should work with ac3 sound, but im not 100%. Check it and find out.

Been really busy, little time for a guide but will see what I can do.

Good luck.

[videocheez]

I finally had success, thanks for your suggestions. The thing that I tried differently was to save the avi out of vdub with no audio checked. This was the only difference. I encoded with cce the avi that had no audio. I used gold wave wav to save out the wav and converted it to ac3 using ac3 machine. I muxed them with tmpge simple multiplex and evertything was good. It took me a month to succeed at this sync. problem. I was about to give up.

Thanks for the guidance,

VC

[Russell_hq]

Congrats on getting your sync issues fix, I know they can be a real pain sometimes.

[andash]

well, i tried both your method, but it is still something strange about the sync. it seems to be fine in the begging of the movie but drops out of sync towards the end. any sugestions?

[Russell_hq]

What type of file is the original movie? Try to separate the audio and video streams. Then test to see how long each stream is. My guess is that the streams are different lengths. When separating the audio, try to convert it to an uncompressed WAV.