Audio Sync

E

Emmaxxx

1
Hi :)
I've been away from the scene for a while and still using old methods to adjust audio\video sync issues when encoding AVI to DVD and was wondering if there were better\easier methods.

Generally if a movie is out of sync consistantly (ie 100ms throughout the movie) this is quite easy to rectify using Vdub or AC3 Delay Corrector to adjust audio timing and then reauthoring to DVD using the extracted audio.
However, if audio is out in two parts of the movie, (ie 1st part is 100ms out and the 2nd half is 200ms out) I use vdub to split the avi to correct each part but then rejoining gives a corrupt audio file.
I use DVD2DVCD to encode to DVD but sync doesn't always turn out right so then I use
TMPGEnc DVD Author for reauthoring when needed.
How can I get a legitimate AC3 audio file where I've had to split into section to correct sync?
Thank you
Emx
 
B

bionic

1
Not much new in terms of methods afaik.
How can I get a legitimate AC3 audio file where I've had to split into section to correct sync?
Click to expand...
I cant reproduce here. Can you give some more info?
Every ac3 file? multichannel files only or stereo too?
Possibly try the vdm surround edition.
http://www.aud-x.com/index.php?option=com_remository&Itemid=34&func=download&filecatid=3
In any circumstance id suggest convert the audio to wav before any editing. Should keep trouble to a minimum.
Or look for another source ;) :)
 
E

Emmaxxx

1
Hi bionic, thanx for your reply.

No, not every AC3 file. I occassionally get troublesome avi's where audio is say, 100ms out for the first half of the movie and 200ms for the second half. The one in question was 5.1. I adjusted the 2 halfs to resync using VDub. Playing back after rejoining the two avi's and sync would be spot on. However, when it then comes to encoding to DVD, there would only be sound for the first half of the film, then silence there after. I've tried demuxing the corrected audio from the avi and just simply reauthoring with the encoded video for my final DVD but the result is the same. I only get issues where I adjust audio sync in more than one section of a film. Obviously there's issues during the rejoining process.
How would I convert to wav maintaining the 5.1? And then correct the sync issue? :)

Yes, looking for another source would be a way around it but not as much fun and satisfying as putting right where someone else didn't do properly in the first place :)

Will take a look at the vdm you mentioned..... Thank you!
 
B

bionic

1
I have a sneaking suspicion its the editing app leaving incomplete frames (during splitting) rendering the ac3 file non dvd compliant.
Can be played as avi fine, but can cause problems during authoring.
Could be the source, could be vdub cutting frames during your editing.

First option, sync with vdm(enable frame mode on).
Theres an option in vdm called enable frame mode, not sure if its in vdub but this option should force it to split in between frames, and should leave the audio compliant.

Second.
Fixing bad frames in ac3 files.
AC3Fix With this you would load the whole ac3 file.
I have to put the ac3fix.exe in the same folder as the ac3 file im working on for it to execute properly.

Theres also Delaycut With this you would need to load the audio from the synced avi parts and cut away the garbage in the header, before remuxing and joining. Havent used it myself so... :)

Third.
To convert ac3 5.1 to wav and retain channel mapping id use dbpoweramp with its directshow plugin and ac3filter.
To edit 5.1 wavs and encode to ac3 5.1 id use soundforge 9 (any ac3 encoder with 5.1 support should do for encoding).
For playback support of 5.1 wavs id use ac3 filter(options| system tab| use ac3filter for pcm)

Start from scratch. Extract audio from both files.
During playback id take note of the ac3 channel mapping(in ac3filter), then set ac3filter to the same mapping.
Convert to wavs with dbpoweramp(uncompressed and channels etc. as source), should leave you with 5.1(6ch)wavs. Remux and edit sync. Join the avis.
Extract the wav audio from the now synced avi.
Convert back to 5.1 ac3 with soundforge(either via the main window/save as or via the batch converter(tools menu)
This should leave you with a fully dvd compliant ac3 file(although with a slight quality loss)

Any questions...? just ask :)
 
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E

Emmaxxx

1
Well, that was all a bit too easy....
Tried option 1 (VDub surround) by splitting the avi into 2 halves to beginin correcting the sync for each. The playback of these were strangely in perfect sync..? So I simple rejoined with vdbsurround and again perfect sync. The proof however would be in the encoding to DVD (DVD2SVC) and again surprisingly no sync issues.
So, I'm puzzled to how this could correct itself by not doing anything?

Anyway, you've given me some useful tips for another time if i'm not so lucky :) Thanx for that!

x
 
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