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In my 3.5 minute video, the rendered video is slightly behind the audio at the beginning. Then near the middle it is synchronized, and then gradually the video gets ahead of the audio. I have tried rendering in various formats, with AV synch on an off, but nothing helps. I am new to video editing, so please include lots of detail in your reply. Thanks

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You should provide more details: general info (version of Blender, operating system) but also specific info (extension/codec of video file, source, frame rate, ...). You can easily get this information from a program like Mediainfo; see https://mediaarea.net/en/MediaInfo)

Your problem is probably that your 3.5 minute video has variable frame rate (eg shot from a smart phone). In order to compress a video, sequences with less action (eg still images) use a smaller framerate (less frames per second). The audio however uses a constant framerate. That's the reason that the audio is drifting away from the video. A more profound explanation is found at https://www.youtube.com/watch?v=keA2Gyye-D0.

You can check the framerate with the forementioned program Mediainfo. This should show something as:

Example of variable frame rate video

Your solution of AV synch does not help because this option only helps in previewing the movie within Blender, making sure that the audio is in sync with the video by dropping some frames while previewing, if Blender can't catch up with the frame rate. Also, changing the output formats doesn't help because the problem is with the input video file; which is probably variable framerate (check this with mediaInfo!).

The solution thus is changing the framerate from variable to constant. You can do it with a program like Handbrake. See, the forementioned video for a in-depth explanation of the procedure.

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  • $\begingroup$ Husch, thankyou so much for your thorough explanation. I will try those things. Knowing that the problem is input and not output should be a great help. $\endgroup$
    – Murv
    Nov 21, 2020 at 17:31
  • $\begingroup$ It worked! Thanks again for your thorough explanation and the links. The video youtube.com/watch?v=keA2Gyye-D0 , and the software mediaarea.net/en/MediaInfo and <Handbrake> were very helpful. $\endgroup$
    – Murv
    Nov 21, 2020 at 19:25

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