Trouble with videos exported/saved from Avidemux (picture is all gray)

[n8skow]

Greetings

I have a video that is split into 6 separate files (mp4) - and I'm using Avidemux 2.6.12 to append them and save out the combined file (also mp4). Video and Audio output are set to 'copy', and I can preview the file within Avidemux just fine. However - the finished file that is saved out plays about 1/4 of the way thru the movie - and then the picture goes all gray (sound continues to play fine). I typically use VideoLanPlayer to watch movies - but notice the same results in other players as well.

What is going on?

[mean]

Maybe encoded with different settings
The encoder settings is global to the whole file

[n8skow]

Seems to be fine if I save to .avi instead...
Any ideas why mp4 is not working though?

[mean]

settings are repeated at each keyframe in avi