I always wondered about this. I have the same TV series as local MP4 files: one with English audio, and another with Greek. I thought I could just extract the audio tracks and use them to build an MKV file with multiple audio, but it always ended up with an audio sync error. One track would always be in sync at the beginning, but 20min in could be out of sync by as much as 5seconds.
How do people build multi-audio files if the audio tracks aren’t part of the original source?
The desync issue is probably caused by different frame rates. For example, an American movie is 60 FPS, while a Greek one is 50 FPS. That leads to a slow desyncining of the audio throughout the video.
If you know about this problem, then I think it’s quite easy to fix while merging the two files.
I think you need to manually adjust the length of the audio stream after you extracted it, they are usually of the common fixed sample rates (like 44.1kHz or 48kHz) and are not tied to the frame rate of the video stream (other than being the same length in time).
For such a small percentage change (a few seconds over something like an hour long) “Change Speed” in an audio editor should be good enough, the shift in pitch should not be noticeable.
I always wondered about this. I have the same TV series as local MP4 files: one with English audio, and another with Greek. I thought I could just extract the audio tracks and use them to build an MKV file with multiple audio, but it always ended up with an audio sync error. One track would always be in sync at the beginning, but 20min in could be out of sync by as much as 5seconds.
How do people build multi-audio files if the audio tracks aren’t part of the original source?
The desync issue is probably caused by different frame rates. For example, an American movie is 60 FPS, while a Greek one is 50 FPS. That leads to a slow desyncining of the audio throughout the video.
If you know about this problem, then I think it’s quite easy to fix while merging the two files.
Yeah that’s what I figured, but I have no idea how to adjust the frame rate when extracting the audio stream :-(
I think you need to manually adjust the length of the audio stream after you extracted it, they are usually of the common fixed sample rates (like 44.1kHz or 48kHz) and are not tied to the frame rate of the video stream (other than being the same length in time).
For such a small percentage change (a few seconds over something like an hour long) “Change Speed” in an audio editor should be good enough, the shift in pitch should not be noticeable.
https://www.youtube.com/watch?v=pkPF8uN0bE8
I’ll give that a try, thanks!