The VideoLAN Forums

I was recently asked what the difference between files using the .mp4, .m4v and m4a were. My understanding is that they were essentially the same container, but with a filename hint to indicate whether the main content is video (m4v for video and m4a for audio, with mp4 being generic). Reading other sources suggest that m4v is a slightly different format that allows support for Apple's DRM, but I am not sure I am convinced this is at the container level and instead an MPEG4 container 'atom'.

Can anyone who is more intimate with MPEG4 specification in general, clarify what the real story is. I just want to validate or adjust my assumptions.

From another source, they are same thing, except Apple expects the m4v extension for certain features to work. Such a shame they depend on the file extension for this. m4a and m4v can be used as content hints (audio/video), with mp4 being the catch-all generic MPEG4 container file extension.

My understanding is that they were essentially the same container, but with a filename hint to indicate whether the main content is video (m4v for video and m4a for audio, with mp4 being generic).

Apple expects the m4v extension for certain features to work.

That's what I have in mind too. I think there is no major difference but the atoms being used. When using an hex editor to watch inside the file I can't see any structure difference.

That's also what this FAQ thread is saying:
http://forum.doom9.org/showthread.php?t=62723

But, I'm not a specialist of containers structures and maybe there have been some evolutions (some new codecs have been accepted so why not something else), so you may want to ask confirmation in this Doom9 thread and/or ask Zenitram, the developer of MediaInfo, in this thread:
http://forum.doom9.org/showthread.php?t=96516

Are you sure you aren't confusing .mov and .mp4?

Use an hex editor and check yourself the header difference between MP4, M4V, M4A, M4B and M4R

All of them are the same, based on ISO format.