How to properly sync two videos

[Filippo]

Hello,
I have a low quality video with audio in my language (converted from 25fps to 23,976) and a 1080 23,976fps video in foreign language (I remove the audio channel). I'm trying to "mux" the audio in my language with the 1080 video.

In premiere I create a sequence in 23,976fps. I cut the videos at the same change sequece at the start so that I can align them as some video have more black at the beginning. Here I can already see the 1080p video is longer of about 4 seconds.

So, I have two video channel and an audio. I keep the smaller video on top so I can see if they're in sync.

The problem is that the video goes out of sync after few change-sequence. I tried adjusting the speed of one timeline so that the two video were the same length, they match the start and end but they go out of sync in between.

I've also tried looking for each scene if there were additional or missing frames and started to "cut" , but after few scenes the shorter video starts to change before the longer, it looks like they havve different "speeds" .

Is there any tool or setting I should look for for this kind of task? The movies are identical and have the same fps but somehow they're different and I don't understand how.

Thank you

[davexnet]

I did a movie like this using audio from a different source using Avisynth and Vdub2. See this thread for details
https://forum.videohelp.com/threads/410976-Syncying-movie-sound-when-one-video-is-slig...ght=delayaudio

[Selur]

Can't tools like Adobe Premiere Pro do something like this nowadays?

[mayazir]

I had a similar task to do - 2 different video files in different languages and I wanted to keep the best of 2 video files and add 2 audio tracks in it. Both files had a different bitrate and different points where I cut ads, so they were not synchronized at all.
I used Sony Vegas, you can also do it with Wondershare Filmora.
Open 2 video files, then move, cut, and move again the 2nd video (using its audio track and adjusting it according to the main video).
If it is a movie, pay close attention to people's lips to synchronize the sound.
I used to cut and move the audio track 5-6 times in 30 min episode (after each scene).
Finally, I even learned to read lips (like deaf people do).
After you synchronize it all, keep the only audio track and add it to the best video file (with Avidemux for example).

[Ennio]

The movies are identical and have the same fps but somehow they're different and I don't understand how.

It may have something to do with differing timestamps in elementary streams and/or on container level.

May I ask which video-codecs the videos are encoded with?