Audio processing and resynchronization

Topics about the audio side of Openshot.

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Audio processing and resynchronization

Postby edaverill » Thu Oct 17, 2013 10:28 pm

I had expected to be able to strip the audio from a recording of a speech, clean it up, bring it back in to openshot as an mp3, and have audio line up. It did not. The synchronization over a 1-hour talk started in sync, but across the program was off by differing amounts up to 4 or 5 seconds. I don't even have the impression that the error was monotonically increasing. It seemed to be closer at the end, than the middle.

The process that failed was to use ffmpeg to strip the audio off the original, process it in audacity until I liked it, export it again, then in openshot bring in the original video and the reworked audio as 2 tracks. There was a delay between the two, but I was able to align the beginning manually. Because of the lack of cues on the audio track, I found it possible to do the alignment only where I could see the beginning of the track in highest magnification. But, bottom line is that the audio did align satisfactorily AT THE BEGINNING, but wandered throughout the next hour.

Messed with it in a variety of ways. Finally, what I did was to edit the video the way I liked it with openshot, keeping the original audio, and export. Then strip off the audio from the openshot output with ffmpeg, rework the audio with audacity, then using the "-audiofile" option on mencoder, replace the original audio with the newly re-worked mp3 on a copy of the openshot output.

That aligned, perfectly, throughout.

So, it is very much my impression that it is openshot's libraries that don't keep track of time, quite right.

If it did, then it would very much be nice for it to show visible audio envelopes like audacity does.

I have version 1.4.2, having failed to find an RPM for 1.4.3 for OpenSuse 12.2
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