Video change speed and lose audio sync after export

I try to change the speed( x1.042000) in video properties to match the movie subtitles, the audio is in sync while editing, using VLC to watch the exported mp4 file, the audio is in sync at the beginning, but gradually out of sync.
I use Shotcut to check, and find out while editing, although the audio is in sync with the video the whole way, but the audio waveform is gradully out of sync. As in the picture below: the gun shoot frame is at 01:25:36, but the gun shoot audio waveform is at 01:25:38.

How is that the sound not matching the waveform? Is it a bug or something else?
Thanks for any input.


If you want to speed up the video you have to resample (speedup) the audio too or
you can split up and cut audio and video and sync it manually.
Maybe it is easier to edit the timestamps for the subtitles.

You can speed up video by just changing the waiting time between the displayed frames. In audio you are limited to standard sampling rate. To archive the speedup by 1.04 you need a resampling filter set. This setup needs a bunch of FIR low pass filters with the same low pass behavior but with slightly different output delay to archive your goal.

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How was the original video on the timeline created? It might be variable frame rate or a dreaded TS container.

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I just found out that in editing mode(moving the cursor), shotcut will force the audio in sync, but in “play” mode, it will gradually lose sync( as in the waveform).

Yes, I am editing the subtitles timestamps now.

I think you are correct. It is from emule.

“Convert to edit-friendly” might fix it.

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No luck. Thanks anyway.

Finally, I just need to detach the audio track and adjust the speed in the audio properties to match the video. FIXED!