how can I mux 25 fps audio into 23.438 fps (1024 spf) ?

[precipizio]

Hi, I have two videos with different fps as in screenshot.

Could you explain me what is spf and why fps of audio file 2 are so much?
How can I mux audio of file 2 into file 1 synchronizing the speech?

I'm on linux so I'd prefer to use linux tools, like ffmpeg.


[Attachment 52753 - Click to enlarge]

[ProWo]

Assuming that both videos are (should be) the same, I think that the left video & audio (1) is the original, the right (2) has been converted (23,970 fps to 25 fps) and this audio has been incorrectly converted.
For a correct conversion of both the video and audio tracks use my clever FFmpeg GUI.
https://www.videohelp.com/software/clever-FFmpeg-GUI

[johns0]

The audio has nothing to do with fps,it's the length that's important,if both tracks are the same running time then both audios will match.

[Cornucopia]

...and they do not match.
There's almost a minute difference between those 2 clips. no amount of "merging" or "muxing" is going to fix that. you need to edit one, the other, or both, in a normal NLE, to even get to the point where they'll sync.

Scott

[johns0]

I would try playing the audio with the video to see if it does go out of sync,if it does it might be very easy or very tough to fix since it could be adjusted by stretching the duration or shrinking it to match and if that doesnt work then there might be a spot where the scene isn't exactly the same and the audio has to be adjusted for that scene and other scenes if needed.

[precipizio]

I summarize what I would like to do because I changed a bit the topic: I'm working with a foreign video (file1) with a better quality (a rare BD remaster) and a video ripped from a DVD of my country (file2) with a lower quality, so I decided that I want to preserve audio2 quality and adequate video1 fps in order to be the same of video2 and then I'll cut audio2 if it's needed.
What is the best way to adapt file1 fps with ffmpeg preserving as much as possible video quality?
thanks for your patience.

[ProWo]

The audio has nothing to do with fps,it's the length that's important,if both tracks are the same running time then both audios will match.

If you have a movie 1 (video720p & audio-eng) with 23.976fps and the same movie 2 (video480p & audio-ita) with 29.97fps and you want to use the audio2 with video1 the you have to convert the audio2 to match the lenght of video1, g.e. 29.97fps to 23.976fps. This can be done with my clever FFmpeg-GUI.

[precipizio]

yes, but I'd lose audio quality, I prefer speeding up/down the video or anyway "modify" the foreign video to fit the audio track and not the opposite.

[smrpix]

yes, but I'd lose audio quality, I prefer speeding up/down the video or anyway "modify" the foreign video to fit the audio track and not the opposite.

That's backwards. It's much easier to adjust audio "transparently" than video.

Convert the audio to uncompressed wav, modify it in an NLE or DAW and convert the final product back to whatever format it needs to be.

[sneaker]

That's backwards. It's much easier to adjust audio "transparently" than video.

I disagree.

1. Drag&drop both files into MKVToolNix GUI.
2. Deactivate audio track of file 1 (23.976 fps file)
3. Set video track fps to 25
4. Mux

Done. (Unless there's some constant delay remaining or the movies are different cuts to begin with.)

[precipizio]

That's backwards. It's much easier to adjust audio "transparently" than video.

I disagree.

1. Drag&drop both files into MKVToolNix GUI.
2. Deactivate audio track of file 1 (23.976 fps file)
3. Set video track fps to 25
4. Mux

Done. (Unless there's some constant delay remaining or the movies are different cuts to begin with.)

It works perfectly, thanks !!

[smrpix]

I see. So the audio and video weren't actually different lengths, just different calculations based on assumed frame rates. Neither the audio or video had to be changed.

[Cornucopia]

IOW they were mis-flagged.

Scott