Audio/Video Syncing Question

[goldensun87]

Ok so, I have a music video, but the audio quality is unsatisfactory. So, I found a video with the same song, and the audio in this video is good, but the video is not a music video, it's just a single-pic slideshow. Anyway, I want to combine this good audio with the video song, but I have a problem. The music video is 24 fps, but the good audio's source video was 29.97 fps. So, my question is, by how many milliseconds do I have to delay the 29.97 audio, to make it sync with the 24 fps video?

[tebasuna51]

Maybe you don't need nothing, maybe you need a delay and/or stretch the audio.

We can't know what you need only with video fps data.

[hello_hello]

Often a 24fps video (more accurately 23.976fps) will have the same duration as a 29.970fps version, just less frames and therefore a lower frame rate, but the duration is what matters. Assuming the audio is the same length and plays at the same speed and it's been edited the same way in each case, they'd be interchangeable. Setting a delay would only hep if the videos don't start in exactly the same place.
If the audio slowly wanders out of sync because the audio/video plays at a slightly different speed you could try adjusting the frame rate a little, or adjusting the frame rate in combination with an audio delay if need be, or they mightn't match up at all. Trial and error.

[goldensun87]

I don't know how to modify the audio to sync with a 24 fps video. I may be able to modify the framerate of the video to sync with the audio (I have black bars to crop anyway). But, should I use Convertfps or Changefps?

[hello_hello]

When I referred to adjusting the frame rate I was referring to doing it while remuxing (not re-encoding). I don't know the format of your source but MKVMergeGUI can open lots of file types and save the output as MKV. You can also use it to adjust the frame rate. Both programs also let you specify an audio delay if need be. I was referring to a 23.976 to 23.974 type of adjustment though (as an example) if the video and audio durations are just slightly different.

ConvertFPS keeps the original duration by using frame blending to increase or decrease the frame rate. ChangeFPS just drops or duplicates frames. No blending, but it mightn't be as smooth.
AssumeFPS keeps the same number of frames but changes the frame rate, and therefore the duration. The result would be the same as changing the frame rate after encoding as I described above. You'd probably want to use the remux method to find the required frame rate and then re-encode using AssumeFPS as it'd be trial and error to get it right.

That's assuming you can get the audio to sync. The second video may have been edited slightly differently. Even if they had the same frame rate it only takes an extra frame or two here, or a frame or two less there, and while the videos may seem to be the same, they're not.