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I downloaded a clip from 56.com or youku.com, and then found that the video and audio is out of sync. At first, near 6:00, the video is about 0.7 second slower, and I used iMovie to "detach audio" and then drag the audio to play 0.7 second later and saved the video. However, I found later that at around 50:00, the video was about 4 to 5 seconds slower. So the video is constantly slower, not by a fixed amount. (I suspect that it is some 23.97 or 24 frame per second issue, but 4 seconds out of 50:00, and that is 0.13% off... (and 23.97 vs 24 is also 0.125%, so they seem quite close).

Is there a way using HandBrake, iMovie, Final Cut Pro, or any other tool to fix it? I only saw that in iMovie, I can set the video to play at 101% speed, but then it will be too fast.

  • Final Cut will at least ask you if it's uncertain of the clip's frame rate, but you have to guess & keep re-importing then deleting til you find the right one. I don't know anything else with even that amount of flexibility. The fault is likely in the [re]encoding in your source video. – Tetsujin May 1 '15 at 10:45
  • actually, it seems that no matter I choose 23.98 or 30, the out of sync amount would be the same – 太極者無極而生 May 1 '15 at 11:11
  • you can type any number you wish in FCP, btw, you're not limited to 'known' formats. Having said that, if it slips at all frame-rates, then there's a chance the original file was saved that way. Only way I could think to change it would be split the soundtrack out to an audio app that can do time-stretching separately from the picture [Cubase can do it, idk of any freeware app], then reimport it to FCP. – Tetsujin May 1 '15 at 11:16
  • oh that might be better. I am right now trying this: detach audio, and click on the video clip and choose Modify -> Retime -> Custom Speed and type in 100.13 in the box and press Enter. It appears as 100 again but the duration below will shrink by 4 seconds. This way I can make it sync better, but there seems to be a granularity of 4 seconds. So if I type in 100.08, it still would show as 4 seconds shorter, instead of only 3 seconds shorter. But it is strange... if I keep on trying different numbers, sometimes I can make it 5 seconds shorter... so it is a bit random – 太極者無極而生 May 1 '15 at 11:26
  • FCP's never been that great with audio. Granularity in something like Cubase is 'sample'… quite some difference ;) – Tetsujin May 1 '15 at 11:30
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I made a workaround which works for short clips: at around 5:00 i split audio and resync second part (drag it backwards by around 0.4s so that is overlaps a little with 1st part). If clip is longer than 10 min I repeat operation at around 10:00; split audio again and resync 3rd part, and so on.

You can do it also for longer clips but it gets more and more tedious

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