The movie header of an MP4, found by walking the file's own boxes: a moov box
after the media is read where it is, and the bytes moov/mvhd inside another
box's payload are not the header. A file with no moov, no mvhd or an mvhd
cut short throws ClipMp4ReadError.
The movie header of an MP4, found by walking the file's own boxes: a
moovbox after the media is read where it is, and the bytesmoov/mvhdinside another box's payload are not the header. A file with nomoov, nomvhdor anmvhdcut short throwsClipMp4ReadError.