Does the M4V file type have direct support for Audio?

Question

I am working with a video vendor who just ripped a dvd and sent me BOTH m4v files AND aac files (audio and video separately),. When I asked him why he did not just send 1 m4v file with the audio and video in ONE FILE, he wrote me back this (Which I need to confirm is true or false):

.M4V is a video format that doesnt directly support audio so the computer automatically rendered the audio files out as .AAC. What you say is an .MP4 format is really just the "file type" and not the extension itself.

Doesn't sound quite right, but I am not a video pro. But I do not want to have to splice all these files together again.

Please advise: Is his statement (above) correct?

Thanks, sleeper

Answer 1

I find the m4v extension a bit confusing.

For MPEG-2, the .m2v extension is associated with a raw video stream. Those files can have only video.

Now for MPEG-4, Apple uses the .m4v extension as a container format, and in fact if you rename an .m4v file to .mp4 it is likely to play on players that only read .mp4 files, since the two format are essentially equivalent.

I think you would need to check this .m4v file and make sure it is really the container format, and not an elementary video stream similar to what you find in .m2v files for MPEG-2.

If you feel comfortable inspecting files with a hex editor, just open this .m4v file, skip the first four bytes and check if the next four are the letters 'ftyp'. If they are, then you have an MP4 container file that should have no trouble holding audio along with the video. If, on the other side, you've got something else, then you may have an elementary stream, in which case you may want to recommend to your vendor to use a different extension for these files. Using .avc is probably more appropriate for an H.264 elementary stream.