Quicktime MOV file from a Panasonic GH3.
Try to mux this source into an MP4. The video can be copied but the audio must be encoded since avidemux does not support PCM in an MP4 file.
Choose copy for video and any AAC codec for audio (lav or faac).
The audio is trashed sound wise and the duration is also shorter than the length of the clip. In the example below, a 30s clip the audio only comes out 15s.
Avidemux 2.6.7 64-bit on Windows 7.
You can get a sample file at this link. The first one, video 1, with the train will suffice.
http://www.dpreview.com/reviews/panasonic-lumix-dmc-gh3/9
On another note: Why is PCM not supported for MP4?