Audio Sync, view waveform?

Discuss about generic usage of MediaCoder.

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JonSmith
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Audio Sync, view waveform?

Post by JonSmith » Thu May 15, 2014 3:02 am

Hi,
I was wondering if anybody knows a way of viewing the audio waveform of a video file (with a timeline)
Whenever I use mediacoder to compress videos to MP4, LC-AAC, X.264 there is usually a audio delay of between -50 & -350ms. At the moment I encode the first few minutes then watch the video in VLC and alter the delay until it sounds right and then encode the whole file using the same delay. This is a bit hit & miss and quite difficult if there isn't a clear sound to sync with, like a door closing.
This got me thinking that if I could view the audio waveform of the before and after video it would be easy to see the delay. Is there a free program to that can do this?
I guess I am making an assumption that it is the audio that is out of sync with the actual timeline, if the video is out of sync with the timeline this wont help.


Thanks.

meRobs
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Re: Audio Sync, view waveform?

Post by meRobs » Thu May 15, 2014 8:54 am

JonSmith wrote: I guess I am making an assumption that it is the audio that is out of sync with the actual timeline, if the video is out of sync with the timeline this wont help.
Surely it is a relative thing. You cannot speak of either stream being the only one out of sync.

I suggest you have a read of the Guide on (free) Editors listed under Tips & Guides.
Have you checked out the Tips & Guides for MediaCoder? Try: http://forum.mediacoderhq.com/viewtopic.php?f=17&t=8061
Also, get older builds at: http://www.videohelp.com/tools/MediaCoder/old-versions#download

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HuggiL
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Re: Audio Sync, view waveform?

Post by HuggiL » Thu May 15, 2014 7:27 pm

SubtitleEdit can generate the waveform of a movie's audio stream. Primarily there to help sync subs to the audio but I'm pretty sure it works without needing a sub file. In any case, I don't know how you'll be able to tell whether if the audio is being delayed or if the video is just faster.
Also, I've never had an issue with MediaCoder creating delays with those settings so it might depend on the source file.
In theory, theory and practice are the same. In practice, they are not.

Tips & Guides: http://forum.mediacoderhq.com/viewtopic.php?f=17&t=8061
Older versions: http://www.videohelp.com/tools/MediaCoder/old-versions#download

JonSmith
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Re: Audio Sync, view waveform?

Post by JonSmith » Fri May 16, 2014 3:58 am

Thank you, I will give SubtitleEdit a try.
The worst files for going out of sync are WMV's
It is quite easy to check the video for delay/advance, I can just play it in pretty much any editor program that shows the time in milliseconds and match a frame of the before and after videos (a simple screenshot of a frame from the "before" video and match it to the "after" video) . My plan is to do similar with the audio wave form then a simple bit of maths should give me the value I need for the audio delay, that's the theory anyway.

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