I've managed to fix NX ('fixed' font had disappeared), and so I tried to pare down a video to make a sample clip.
Using avidemux on this DishNetwork H.264/AVC transport stream, when I try to save the edited clip it fails with:
The beginning frame is not a key frame.
Please move the A marker.
Of course you're supposed to use the double-arrow to go to the next keyframe, so I set the A marker at the beginning, double-arrow a couple times, set the B marker, and Edit|Delete. Saving still fails the same way.
I can only conclude that the double-arrow does not take you to a keyframe in H.264 and thus avidemux is not compatible with this compression.
I tried playing a second or two, stopping, and deleting before this, but that didn't work either. I don't know what to do.