I don’t think that’s quite right is it? As I understand, mp4 is based on mov. But they still very much are distinct container formats, and an implementation of the mp4 standard would likely not be able to correctly read mov files as is, would it?
They're very close. The ISO base media file format was directly based off of QuickTime container format.
If you look at a .mov file and a .mp4 file in a ISO bmff viewer, you'll generally see the only difference is the ftyp box is different ("qt " for .mov, "isom" for .mp4). Indeed, if you ask ffmpeg to make a .mov file and .mp4 file of the same content, literally the only difference is the contents of the "ftyp" box, every other byte is identical.
> literally the only difference is the contents of the "ftyp" box, every other byte is identical.
Not quite. There are some boxes acceptable in one but not the other. Strings inside MOOV are length-prefixed in MOV but null-terminated in ISOBMFF. There are a variety of differences like that.
The set of codecs allowed, also differs between the two.
They're pretty much interchangable. Video frameworks like gstreamer just give you qtdemux to parse .mov, .mp4, and even .m4a or .m4v (which are just MP4s with different file extensions).