Using theaudio shift option.

[Gandalf]

How do I go about correctly using the audio shift feature in avidemux (I am using version 2.7.3)? I have seen nothing in the documentation that explains how to go about it. Thanks in advance for your help.

[eumagga0x2a]

Enable shift by checking the checkbox, negative values advance audio relative to video, positive ones advance video relative to audio by the number of milliseconds indicated.

[Gandalf]

Thanks. One remaining issue that I would appreciate help with is as follows: I am in the process of attempting to correct a 47 minute video, and the issue that I am dealing with is that the audio and video start out synchronized, but partway through it, the audio part starts to lag behind the video part by as much as about 20 seconds. Any suggestions for resolving that issue will be greatly appreciated.

[eumagga0x2a]

It depends entirely on whether the desync rate stays constant throughout the video and on the FPS value. Please paste the output of MediaInfo and the of the "Properties" dialog in Avidemux for the file into your reply.

As a guess, the most likely scenario which led to this problem was saving a video with 24000/1001 fps frame rate as exact 24 fps, so that re-encoding the video with the "Change FPS" filter applied doing 24.00 --> 23.976 (Film) conversion might restore sync. We'll see once the information about the video has been provided.

(Obviously, don't use AVI to store H.264 or HEVC.)

[Mamecube]

I am in the process of attempting to correct a 47 minute video, and the issue that I am dealing with is that the audio and video start out synchronized, but partway through it, the audio part starts to lag behind the video part by as much as about 20 seconds.

The time shift just pushes the audio forward/backwards at the start. This is mostly to accommodate for adding black or a logo to the start of a video.

If you demuxed your audio and video into raws, you would see your video and audio files are not the same run length. Your audio file is longer.

If the two are coming unsynched, you almost always have to correct the video rather than the audio. The only exception is when you're dealing with PCM audio.