m4v file extensions
by st373n on Sep.01, 2009, under ReduxEncoder
To clarify why I used m4v file extensions in ReduxEncoder for its file extension for apple devices – i quote here from the elgato forum – hope that finally clears up the matter for those who wanted to know or queried my sanity 
“The difference between mp4 and m4v is the extension, the contents are identical. Unfortunately Apple’s software (both QT and AppleTV) enables certain features only if they are presented with a m4v extension, so depending on the features used we change from mp4 to m4v. An example of this is that Apple TV doesn’t play files with mixed AC-3/AAC audio unless they are in a .m4v container.”
“You can safely rename mp4 files to m4v. There is no difference between the two formats. Default association for m4v is iTunes, mp4 is QuickTime. There is a difference in what the Apple TV supports with the two formats as mentioned.”
“I think it’s more accurate to say they’re two different extensions for the same format, And the extension doesn’t necessarily imply the format, which is what a lot of people assume and has become particularly confusing with audio/video formats.”
5 Comments for this entry
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October 26th, 2009 on 7:56 am
I’ve found some problems with this. Take a file encoded to be .m4v (with Handbrake), and rename it to be .mp4. Some files work, but others throw this error in Quicktime Player 7 (which Snow Leopard keeps if you already had QT Pro. The new Quicktime Player allows the file to work.
“An invalid sample description was found in the movie.”
Is the problem with the file or is it with Quicktime Player 7 for handling something slightly unexpected–chapter info in a file named .mp4–poorly?
October 28th, 2009 on 2:21 am
Hey Chris,
I’m not to sure how the Handbreak team are adding the ‘atoms’ to the .m4v files, they may be using a or may have written their own code, probably a better place to ask your question would be over at the handbreak forums.
In ReduxEncoder the tools that add meta data and chapters are atomic parsley and mp4chaps.
Also in order for Quicktime , iTunes AppleTV etc to see the chapters the files need to be m4v, perhaps its your renaming to mp4 thats causing something strange to happen.
November 1st, 2009 on 3:41 am
Love the app! I have noticed one issue that I was hoping you could explain. Whenever I add artwork (movie posters) to the m4v files created by ReduxEncoder, iTunes temporarily freezes while processing this addition. Ultimately, iTunes unfreezes & correctly assigns the artwork.
Is there something about the encoding process that requires iTunes to re-code & thus cause this delay upon addition of artwork?
November 1st, 2009 on 4:05 am
Hey Scott. Yep thats the case for any file you add to itunes regardless of its source, if the files are large it can seem to take itunes a long time.
January 9th, 2010 on 5:39 am
Hello!
The finder tells me a difference between .m4v and .mp4, even if you change the extension afterwards. mp4-Files are called MPEG-4-Movie and m4v-Files are called MPEG-4-Videofile (it should be so, if translated to english, in German it is “MPEG4-Film and MPEG-4-Videodatei).
I.e. the file was originally a .mp4 file (MPEG-4-Movie) and you rename it to .m4v, it still remains to be a MPEG4-Movie and visa versa. So how should the finder know this, if only the extension differs?
As I noticed this, I did not rename from .m4v to .mp4 anymore, but use Quicktime Pro to export to MPEG4 and select passthrough for Video and Audio.
For the other direction, I do not know a “clean” way, but I am not really shure, if that could be needed. When going from m4v to mp4 over Quicktime, the extra data will be lost (I guess) – so better keep the m4v – or if I have an mp4, I don’t think it needs any conversion to m4v.