mythtv@mythtv:~/720p$ MP4Box -add Discovery\ Atlas.720p.HDTV.x264.264 Discovery\ Atlas.720p.HDTV.x264.mp4
Adjusting AVC SizeLength to 16 bits
AVC-H264 import - frame size 960 x 540 at 25.0000 FPS
Adjusting AVC SizeLength to 24 bits
MP4Box: media_tools/media_import.c:3716: gf_import_h264: Assertion `nal_start' failed.
Aborted (core dumped)