MKVToolNix can convert video and audio fps without recompression.

[LMndz]

Hello everyone, first time posting here.

The reason for my post is as follows:

I have always believed that to synchronize audio coming from a PAL source (25fps) to an NTSC or 24p it was necessary to use a tool like ffmpeg to adjust the speed, and therefore it was necessary to recompress the audio, losing time and quality. But after reviewing the MKVmerge documentation, I saw that there is an option to do a “linear” synchronization.

I have used a 25fps video with the AC3 audio correctly synchronized, and converted it to 24fps without recompression and without losing the audio and video sync.

To achieve this, I imported the file into MKVToolNix GUI and changed the following parameters:

-In the video track I have set 24p in the “Default duration/FPS” field.

-In the audio track I have set 0,25/24 in the “Delay” field (delay,old fps/new fps).

After multiplexing I have checked how the video speed is now 24fps and that the audio is still synchronized.


I don't know if this was already known or not, but I've been looking for a way to do it for a long time and I've always found the same answer: change the audio duration and then recompress with the desired codec.


I also don't have the experience to know if using this method the audio suffers any problem, or not. That's why I want others to try it to see if this is the right way to proceed.


Thanks.

[jagabo]

This is old news. The problem is that many players will not respond to the metadata -- especially outside a Windows computer. So it's not a general case solution.

[ProWo]

Try to play this new video on your TV.