Sound out of sync after merging multiple mp4 files with Avidemux

Question

I am trying to join (merge) two or more .mp4 files together, without re-encoding.

Here is what I did:

1. Started Avidemux 2.5.5.
2. With File->Open, selected Input1.mp4.
3. I received this message - "H.264 detected. If the file is using B-frames as reference it can lead to a crash or stuttering. Avidemux can use another mode which is safe but YOU WILL LOOSE SOME FRAME ACCURACY. Do you want to use that mode?". I chose "No".
4. With File->Append, selected Input2.mp4.
5. I received the same "H.264 detected" message again and chose "No".
6. Selected the Format to MP4 (from AVI).
7. Saved the output file (called Output.mp4) with File->Save->Save Video.

Unfortunately, when I play the Output.mp4 video in VLC, the sound is out of sync with the second video. How can I correct this?

Answer 1

I have had much better results joining multiple video files using mkvmerge from the MKVToolNix tools.

Just download and install the windows installer from here. Then run the mkvmerge GUI, add the first file, and then use the append button to add the additional files. This does give you an mkv file instead of an mp4 file, but VLC should be able to play that without any trouble. Also, there is no re-encoding going on, only re-muxing.