Fixing out-of-sync audio

[davecc]

I have an mp4 video/AAC audio file with out-of-sync audio. I downloaded Avidemux which has a "Shift" feature which fixes this type of problem.

I adjusted the shift until the audio was perfect and saved the file. I played the video several times in Avidemux to confirm all was well, then I quit Avidemux.

I then opened up the file in iMovie and played it. The audio was out of sync again, just like nothing had been fixed (about 300 ms).

What gives?

Ideas?

Thanks!
Dave

OS X 10.9 MaverX

[Baldrick]

Is out of sync if you play it with vlc?

imovie might ignore the audio delay/shift.

[davecc]

yes, out of sync, played with VLC, latest version.

[hech54]

I adjusted the shift until the audio was perfect and saved the file. I played the video several times in Avidemux to confirm all was well, then I quit Avidemux.

How did you SAVE the video?

[davecc]

If you're asking how I saved it after editing it (correcting the out-of-sync audio) in Avidemux, I selected Save from the File menu. I was presented with a standard Save dialog, I chose the destination folder, and I clicked the Save button. I didn't change any of the codec details on the main panel (Video decoder: left default of Lavcodec; Video output: copy; Audio output: copy; Output format: MP4 Muxer). At least that's what I think I did -- I tried to use defaults, not venture beyond what I knew. I reasoned that I corrected the audio sync problem and didn't want to change video or audio encoding so I chose "Copy".

Now when I try to save it again, I'm getting an error message that says "Too short. The video was saved but seems incomplete." An "Encoding" pane is also displaying H264, AAC, Mp4 information.

Thanks,
Dave
OS X 10.9 MaverX

[davecc]

Is out of sync if you play it with vlc?

imovie might ignore the audio delay/shift.

Maybe I misunderstand, but I think delay/shift is not just meta data delivered to VLC, but I thought it *stretches* the audio track to match the length of the video. Then when it is saved there is no difference between the 2 tracks (audio & video).

I see either 2 reasons for the delay/shift correction not working:
1. Avidemux did not save the corrected file (ie, maybe I did not correctly save the file), or

2. Avidemux doesn't save a corrected file, but instead saves the original, uncorrected file with some metadata about the sync. delay and only players that recognize this metadata can play it properly.

THanks,
Dave

[hech54]

You should be creating a new file.
Copy
Copy
MP4
....call the new file something like fixedaudio.mp4

[davecc]

I'm sorry I wasn't clear. That is what I did. When savingt I chose a different name than the original file, and selected these options: Copy; Copy; MP4.

So, do you know if Avidemux actually stretches the audio track to match the length of the video track (if I specify the "Shift" feature) and writes out a corrected file when I save? As opposed to saving the uncorrected file and appending some metadata specifying the value of the mis-sync time? (The latter choice is my only explanation for why this is happening...)

Thanks,
Dave

[hech54]

SHIFT changes everything.....it doesn't fix progressively out of sync video. It doesn't "stretch"....it shifts.

[davecc]

OK, it should have fixed it. But it didn't when saved and played on VLC.

What's my next option?

Thanks,
Dave

[hech54]

Is the audio(on the original file) out of sync from beginning to end of the file, or does it get progressively worse/better as the file progresses? Like I said before...AviDemux or any other editor that SHIFTs audio does not fix audio that has a playback rate issue.
I replace audio in music videos almost weekly with better quality CD Audio. It's a hobby of mine and I use Avidemux exclusively for this.
If you are doing what you say you are doing(SHIFTing the audio - delaying or advancing the start of the audio) it will work perfectly....if someone replaced the audio in that file before you....and did it badly(using NTSC audio from a PAL source - or vise versa), a simple SHIFT is not going to solve the problem.
Even someone simply encoding it to MP4 incorrectly can permanently damage the file and ruin the sync.....though that takes a lot of incorrect steps in the encoding process to do.

[Sartori]

Shift it once to align the front of the file , then shift it a second time to align the end of the file (take a note of the time points you aligned to) , extract the audio and stretch it by the difference of the second alignment between the two time points . Recode and remux , I`ve done it a few times with concert videos after I`ve got hold of a better audio file .

[davecc]

Ah! Hech54: audio was in-sync early in the file but out-of-sync at the end.

I misunderstood the Shift function in Avidemux. I was shifting the audio until the audio at the end of the file was aligned. I didn't notice that the audio earlier in the file is now out-of-sync (much of the beginning is voice-over -- no talking heads).

So, the audio needs to be "stretched".

Sartori: what utility(ies) are you using when you say you align twice, extract and stretch the audio?

Thanks!

[Ryan Petrus]

**For sync up multiple camera angles, I'd suggest trying out*PluralEyes (http://pluraleyes.com).
And*if you're just shooting on 1 camera, check out*DreamSync (http://dreamsyncapp.com). It's not as cumbersome or expensive as PluralEyes and gets the job done for smaller quick projects.*

**There's acutally an app called DreamSync, a standalone application that's built for the novice user as well as professionals. It syncs your footage and audio into one single clip so that it can then be imported into applications like iMovie, Windows Movie Maker, Adobe Premiere, Final Cut X, or any other editing suite.*
http://dreamsyncapp.com
Both apps are effective depending on your editing workflow and how much (or little) time you want to dedicate to learning another interface for syncing audio/video footage. *

[donestes]

DreamSync sounds really good, but it's Mac only.

Plural Eyes appears to work great at syncing multiple audio tracks, but does nothing for out of sync audio/video.

Any other suggestions? This has become an immediate issue as I need to post some videos for business.

Thanks in advance.