Audio Sync Problem

[lwea2009]

Hi,

I have recently ripped a lot of my DVDs to digital form, using an app called Handbrake, using my macbook. The DVDs were a mixture of NTSC and PAL, which I ripped to mp4 (h.264 acc).

Now, i've recently noticed some of the ripped mp4s have audio out of sync by a second or so, which gets worse towards the end of the movie.
Upon examining the troublesome mp4s, I noticed the audio track was slightly longer than the video track. I believe this was caused by encoding the NTSC movies at a different framerate to the audio track, probably a setting I could have changed in Handbrake had I known

The problem is, I binned all the DVDs once I ripped them, so re-ripping is out the question.

Is there a way to extract & compress the audio track, so it matches the length of the video track, or maybe even change the video length by altering the framerate?

Any help is much appreciated :P

[tomlee59]

Such sync problems are unfortunately too common. If the rate of sync drift is truly constant, then it is straightforward to fix. The basic outline of what you need to do is:

1) Rip your disc as a single vob. Here the ripping is incidental; it's the creation of a single vob that's the main goal.
2) Demux to extract your audio track.

(I believe that DVD Decrypter will perform both (1) and (2), but it's been too long for me to remember for sure. There are many other choices as well.)

3) Use Audacity or other favorite audio tool to change the duration as necessary. Audacity has a "tempo change" feature that does exactly what you need. Just be sure that you have precisely characterized the sync error -- you need to get to sub-100ms accuracy. You can use VLC or mplayer to find the precise numbers to shoot for.

4) Remux the fixed audio with the video, test the result for sync, then re-author the combination as a DVD if all looks good.

[lwea2009]

unfortunately i do not have the discs anymore, just the ripprd mp4s

i might have a play around with quicktime pro, see if i can export the audio track, compress it (with audacity?), then import it back into the mp4 file with quicktime pro again.

[tomlee59]

unfortunately i do not have the discs anymore, just the ripprd mp4s

i might have a play around with quicktime pro, see if i can export the audio track, compress it (with audacity?), then import it back into the mp4 file with quicktime pro again.

Just to make sure we're talking the same language, understand that "compressing" implies a file-size reduction to most computer folks, and a dynamic-range reduction to audio heads. You want to change duration, so let's just call it that.

Any method that you have to separate audio from video, and then recombine the two will get you most of what you need. it doesn't matter that you only have the mp4 version left.

"MP4" is known as a "container format," so by itself doesn't tell us much. MP4 video and audio can be encoded a number of different ways. Audacity will read pretty much all of the supported audio formats, with the possible exception of AAC (AFAIK) and some relatively obscure voice-only codecs. As long as your vid doesn't use AAC audio, then Audacity's tempo change feature will fix your sync problems.

[greymalkin]

unfortunately i do not have the discs anymore, just the ripprd mp4s

i might have a play around with quicktime pro, see if i can export the audio track, compress it (with audacity?), then import it back into the mp4 file with quicktime pro again.

buy the disks cheapskate.

and read the rules before posting.

[lwea2009]

Actually, i did own the genuine DVDs all in a big sleeve wallet holder (couple of hundred dvds), but i decided that it would be better to store them on a hard-drive.

I threw away all the discs after ripping them, as i thought i had no more need for them.

All i'm looking to do is to get the audio track (aac i believe), to match the length of the video track (h.264), contained within a .mp4 file.

I'm guessing its a case of extracting the audio file (demux?), then shortening this file somehow, then importing it back into the .mp4 file, hopefully now in sync.

Surely someone has done something like this before?

Cheers

[orsetto]

I have found Handbrake gives the *least* number of issues with sound sync, in fact not once has it given me a problem. Unfortunately it takes forever to do its conversions, so I often lose patience with it and opt for other software that converts in a fraction of the time but with some risk of audio sync drift. Whenever I notice really bad sync drift, I re-rip those DVDs using Handbrake and the sync comes out perfect. But since you were ripping both PAL and NTSC discs the Handbrake settings may have needed adjustment, that might be what caused your drift (I've only used the default NTSC settings myself). Try the suggestions tomlee59 offered to fudge the audio track in your files, that should work.

BTW this is a good example of why you should NEVER dispose of the original DVDs: you never know when you might need to re-rip them, file formats come and go, and hard drives do fail. If you really have no use for the DVDs other than backup, store them in 50-disc plastic cakebox spindles, the way blank disks are sold. They take up no space this way, and they are protected. Its much better than tossing them and losing the option to reuse them.

[tomlee59]

Actually, i did own the genuine DVDs all in a big sleeve wallet holder (couple of hundred dvds), but i decided that it would be better to store them on a hard-drive.

I threw away all the discs after ripping them, as i thought i had no more need for them.

All i'm looking to do is to get the audio track (aac i believe), to match the length of the video track (h.264), contained within a .mp4 file.

I'm guessing its a case of extracting the audio file (demux?), then shortening this file somehow, then importing it back into the .mp4 file, hopefully now in sync.

Surely someone has done something like this before?

Cheers

Yep. That's why the workflow suggestion is what I wrote: Demux, fix audio, remux.

Search the Tools section of this forum for what you need. MP4Muxer will mux and demux. Audacity -- mentioned before -- will shorten the audio track's duration. These are all free tools. Why not just try them?

[lwea2009]

just an update

been experimenting with AviDemux, changing the audio framerate (PAL/film), and the video frame rate, but it still seems out of sync.

i have looked at some other mp4s i encoded using Handbrake that are in sync, and they have the audio and video at different lengths aswell, so i believe the problem is to do with the video framerate, not the audio track length.

i shall experiment furthur with changing the video framerate...