EyeTV Lounge • View topic - Why sometimes a .mp4 file and other times a m4v file?

by **Mike Evangelist** » May 13th, 2009, 3:28 pm

This question comes up pretty often, so I asked for some clarification from our engineers.

Why does Turbo sometimes create a mp4 file and other times a m4v file?

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.

by **Ron Priest** » May 13th, 2009, 3:56 pm

Mike Evangelist wrote: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.

Thanks for that info Mike. So I wonder what would happen then if I had a .mp4 file that did in fact have mixed AC-3/ACC audio and I manually renamed the file extension to .m4v? Would QT player or iTunes pay it or would my computer just self destruct ya think?

This brings up another question. Why does eyeTV and turbo.264 HD name iPod files differently. It appears that when converting .eyetv files to an iPod file inside eyeTV (with the turbo.264 hardware installed), the eyetv produced file will receive a .m4v extension. However, when dropping that same .eyetv file directly into the turbo.264 software it delivers a file with the .mp4 extension? I'm aware that you can assign what ever extension you desire, but those are the default settings so I tend to just leave them that way until I have a good reason to change them.

by **Judboy** » May 13th, 2009, 4:03 pm

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.

I think .mov will work for the Apple TV and AC-3/AAC audio. I will test, but I believe that it will. Can anyone confirm?

by **sjk** » May 13th, 2009, 8:53 pm

Mike Evangelist wrote:Unfortunately Apple's software (both QT and AppleTV) enables certain features only if they are presented with a m4v extension, …
Apple TV doesn't play files with mixed AC-3/AAC audio unless they are in a .m4v container.

The last part seems confusing because the first part says it's the .m4v extension, not the container, that can matter to Apple TV (sigh). Plus there's no .m4v container; in this case it would be an MP4 container (which supports multiple audio/video formats) using the .m4v extension (a non-standard usage popularized by Apple, according to Wikipedia).

Ron Priest wrote:So I wonder what would happen then if I had a .mp4 file that did in fact have mixed AC-3/ACC audio and I manually renamed the file extension to .m4v

On OS X that would normally change the default app for opening it from QuickTime Player to iTunes. Renaming or removing a file's extension doesn't change its content, but can often influence how it's treated by the system, which I think you understand:

I'm aware that you can assign what ever extension you desire

Why does eyeTV and turbo.264 HD name iPod files differently.

Mike said:

so depending on the features used we change from mp4 to m4v

… which to me implied possible differences in extensions used when exporting from EyeTV or Turbo.264(HD). I'd noticed this but hadn't understood possible reasons for those differences. They can't be more than a best guess at how the output is intended to be used. So, filenames might end up having .mp4 extensions when .m4v would be preferable (for an iTunes/iPod/iPhone/Apple TV context). Seems .mp4 tends to be for a more general QuickTime context, like .mov and .mpg/.mpeg. And there are cases like:

Judboy wrote:I think .mov will work for the Apple TV and AC-3/AAC audio. Can anyone confirm?

I'm curious. Files I've edited with .mp4 and/or .m4v extensions in QuickTime player and saved with .mov that are compatible with iTunes and my iPod touch, but don't contain AC-3 audio.

This is mostly applicable for OS X, to keep things simpler. I'm not sure how files with .m4v extensions are handled by Windows if QuickTime and iTunes aren't installed.

by **Ron Priest** » May 13th, 2009, 9:08 pm

Hummmm... I do notice now that it's mentioned, the default program for a .mp4 file is Quick Time Player, while the default player for .m4v is iTunes.

by **sjk** » May 13th, 2009, 9:47 pm

ddantzler wrote:You can safely rename mp4 files to m4v. There is no difference between the two formats.

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.

.mov will not support subtitles or bookmarks on Apple TV.

That's not a limitation of the QuickTime container format (and its typical .mov extension), which supports chapters and subtitles.

by **Judboy** » May 13th, 2009, 10:03 pm

I encoded for Apple TV using Turbo.264 HD preset. The Apple TV has a feature when playing a movie that has chapters where you can press and hold the play button and the Chapter Menu will appear. Trubo.264 HD does not enable this feature when using Apple TV Preset. I was able to make this work by opening the movie from the Turbo with RoadMovie and selecting Flatten (Keep Current Format) and selecting enable chapters check box and the result was a file with a .mov extension that worked fine with Apple TV and enabled the Chapter Menu and allowed AC3 audio as well.

P.S. It may be all that was needed was for the movie to be flattened to enable chapter menu feature with Apple TV.

by **sjk** » May 14th, 2009, 5:42 am

Judboy wrote:It may be all that was needed was for the movie to be flattened to enable chapter menu feature with Apple TV.

If so, the Flatten Movies Automator action might be useful for doing that.

by **Jon walker** » May 15th, 2009, 5:33 pm

Judboy wrote:The Apple TV has a feature when playing a movie that has chapters where you can press and hold the play button and the Chapter Menu will appear. Trubo.264 HD does not enable this feature when using Apple TV Preset... It may be all that was needed was for the movie to be flattened to enable chapter menu feature with Apple TV.

The chapter track is not currently being linked properly in the file during the MP4/M4V track muxing/mixing process. Basically, QT files can now have alternative audio and/or video tracks each of which can be associated with its own individual chapter text track. T.264 programmers are targeting the chapter text track at itself which the TV device interprets as having no chapter track at all and simply falls back on the "default-20" algorithm which divides the file into 20 equal length chapter segments while most other QT players simply recognize/use the chapter text track as it always has.

Judboy wrote:I was able to make this work by opening the movie from the Turbo with RoadMovie and selecting Flatten (Keep Current Format) and selecting enable chapters check box and the result was a file with a .mov extension that worked fine with Apple TV and enabled the Chapter Menu and allowed AC3 audio as well.

You could also just open the file in QT Pro, point the "Chapter" pop-up for the Video Track to the "Text Track" containing the "Chapter" data in the Properties Window, then select the "Text Track" containing the "Chapter" data, reset its "Chapter" pop-up to "None", and, if you really want to follow Apple's standard recommendation, deselect the "Chapter" Text Track so it does not show up in the Inspector Window. Since iTunes now treats MOV containers the same as MP4 and M4V as far as "Artwork" is concerned, I no longer have any objections to making such minor "tweaks" to T.264HD TV files in order to make them play correctly on the TV device until such time as Elgato corrects this matter.

by **Judboy** » May 15th, 2009, 6:50 pm

You could also just open the file in QT Pro, point the "Chapter" pop-up for the Video Track to the "Text Track" containing the "Chapter" data in the Properties Window, then select the "Text Track" containing the "Chapter" data, reset its "Chapter" pop-up to "None", and, if you really want to follow Apple's standard recommendation, deselect the "Chapter" Text Track so it does not show up in the Inspector Window. Since iTunes now treats MOV containers the same as MP4 and M4V as far as "Artwork" is concerned, I no longer have any objections to making such minor "tweaks" to T.264HD TV files in order to make them play correctly on the TV device until such time as Elgato corrects this matter.

How do you do the above?

by **sjk** » May 15th, 2009, 9:11 pm

Judboy wrote:How do you do the above?

As he described, with QT Pro. I've similarly deleted the Closed Caption Track.

by **Jon walker** » May 16th, 2009, 2:10 am

Judboy wrote:How do you do the above?

For those who prefer/require a graphic explanation of the process, here is a "Quickie" tutorial I just put together:

QT Pro Tutorial 032

Unfortunately, the "the hurrier I go, the behinder I get" and made some mistakes putting together the voice-over. Note that when I mistakenly said to "deselect the file," I actually meant to "deselect the Text Track" as recommended by Apple so as not to include the chapter/text track in the Inspector Window listing. Be advised that this is the normal convention but is not mandatory. The main problem with the Turbo.264 and Turbo.264HD chaptering process is the the wrong track is currently "keyed" to Chapter data. Keying the Video Track to the "Chapter" text track is the correct way to make the TV device recognize the text track generated by Turbo.264.