Difference between .m4v and .mp4?

[Jasoco]

What's the point of an .m4v file extension if the file is the same as an .mp4 video?

The only difference I've seen is that the .m4v files tell QuickTime and iTunes and AppleTV that there are chapter breaks. In QT and iTunes you'll see a pull-down menu to jump to chapters. But if you rename the same file back to .mp4, the breaks disappear. They're still in the file, but QuickTime and iTunes and AppleTV forgets they exist. (Also, .m4v by default opens in iTunes while .mp4 opens in QuickTime. But both can read both.)

What's the point? Why create a new extension rather than just extending QT and iTunes and AppleTV to recognize the chapters??

I mean, it makes no sense. Is there a technical reason I missed? The files are exactly the same. Just the extension is different. You can rename them physically and have them act differently.

[chucker]

The short version: file extensions are, always have been, and always will be, a hugely flawed, broken design. Apple has a far superior alternative in UTIs, but is making the mistake of not proposing it to a standards committee so others (especially the open source community) can embrace it as well. So for interoperability, we're stuck with file extensions, aka teh ultimate sux™, and sometimes MIME types, which are a little better but need to be mapped back to file extensions, making their theoretical advantages just that: not practical.

For MPEG-4 content, the suggested file extension is .mp4. This may seem sensible at first, but is problematic for many reasons.

For instance, .mp2 and .mp3 were both used for audio formats: MPEG-1 Audio Layer 2 and 3, respectively. This is why "MP3" became such a common term to refer to the latter. Many people would thus expect .mp4 to refer to the successor of those, no? Well, a file with .mp4 can be just that: Advanced Audio Coding (AAC) audio content inside an MPEG-4 wrapper. Since AAC is the legitimate successor of MP3, that'd make sense.

Trouble is, most of the time, files with .mp4 as their extension aren't audio; they're primarily video (with typically one or more audio tracks on the side). Apple recognized that weirdness and therefore introduced an alternative designation for audio-only MPEG-4 files: .m4a, for MPEG-4 Audio. (Even more confusingly, there's also .aac, which is also the same codec, but isn't necessarily wrapped inside MPEG-4. It could be MPEG-2 instead, or another wrapper, such as WAV. Wonderful, isn't it?) They then added two more: .m4b for MPEG-4 Bookmarked Audio as well as .m4p for MPEG-4 Protected Audio. Unfortunately, that already doesn't work so well: what if you've got an audio book? It'd be both protected and bookmarked. It's .m4b, confusingly enough. So .m4b can have DRM, but not necessarily!

Finally, Apple added another extension, as you noted, .m4v for video, mostly to remain consistent with their own naming rules. But .m4v again can have DRM, but doesn't need to. There's no ".m4vp" or ".m4pv" for MPEG-4 Protected Video.

By now I'm sure you'll agree: file name extensions suck. Whoever came up with the concept needs a smacking, and Apple needs a major wake-up call to recognize their unique ability and opportunity, right here and now, to introduce UTIs to the world. UTIs are flexible enough that they can describe properties such as "this is protected", "this is just audio", "this has bookmarks", and so on, yet still machine-parseable enough to be cross-platform.

[Eugene]

I like file extensions as a visual reminder of what might be able to play a file. Sure you could have an icon that says "XviD video" or something like that, but playback requirements are increasingly complex. Not everything can decode XviD. Some decoders can't even decode certain types of XviD. Not all XviD is contained in the same container format either...

At this point suffixes are appreciated for analog convenience rather than being functional necessity...

[Schnauzer]

For instance, .mp2 and .mp3 were both used for audio formats: MPEG-1 Audio Layer 2 and 3, respectively. This is why "MP3" became such a common term to refer to the latter. Many people would thus expect .mp4 to refer to the successor of those, no? Well, a file with .mp4 can be just that: Advanced Audio Coding (AAC) audio content inside an MPEG-4 wrapper. Since AAC is the legitimate successor of MP3, that'd make sense.


Man, I am glad to have you back Chucker! I really learned alot from that post about the files type, which I always was a little confused about! Thanks for the great info!
I always wonder though why .jpeg has many different file extensions like jgp

[Jasoco]

Still doesn't explain why they can't modify QuickTime and iTunes and AppleTV to know what chapter markers are. It's weird. They're there, but only seen when the extension is changed. Makes no sense to me. Seems like an easy code job.

[apple007]

If creating a file, does it make any difference if I use .m4v or .mp4 as the extension? I believe both of those are options in HandBrake; if I screw up and use the wrong one, is it really as simple as changing the extension or does something get lost in the change? Thanks.

[chucker]

I like file extensions as a visual reminder of what might be able to play a file.

Ah, but that doesn't really work well either, does it? When you have, say, .avi, how do you know your player actually has the needed codecs? With UTIs, the file manager could say something like "MP3 audio and XviD video in an AVI container".

[Jasoco]

If creating a file, does it make any difference if I use .m4v or .mp4 as the extension? I believe both of those are options in HandBrake; if I screw up and use the wrong one, is it really as simple as changing the extension or does something get lost in the change? Thanks.

Nope. Nothing is lost. You can rip a video as MP4 with the Chapter Markers on and while they get ignored at first, changing it to M4V will restore them. Changing back makes them go away again, but they're still there. Just ignored like a lonely old man begging for change on a street corner..

What the heck did I just type?

[Eugene]

Ah, but that doesn't really work well either, does it? When you have, say, .avi, how do you know your player actually has the needed codecs? With UTIs, the file manager could say something like "MP3 audio and XviD video in an AVI container".
That's why it's nice when distributing a file, that its filename contain some pertinent information. StarshipTroopers.XviD.avi for example.

[StevesMom]

Nope. Nothing is lost. You can rip a video as MP4 with the Chapter Markers on and while they get ignored at first, changing it to M4V will restore them. Changing back makes them go away again, but they're still there. Just ignored like a lonely old man begging for change on a street corner..

What the heck did I just type?

That's a great tip, I have all my HandBrake video in iTunes with .mp4 extensions (no real reason for picking mp4 though, i just didn't see the point in using Apple-specific .m4v until just now) and although the chapter markers are honoured within iTunes, QuickTime Pro, Chroma and NicePlayer just don't pick up the chapter marks.

Clearly that's because I'm using .mp4 as the file extension. Doh ! Time for a mass renaming session, I think.

Thanks !

Sm.

[chucker]

That's why it's nice when distributing a file, that its filename contain some pertinent information. StarshipTroopers.XviD.avi for example.

It's a crutch. File names ought to be just that: names. Titles. That metadata is sometimes put into the name in order to point out important information (such as the used codecs, or perhaps even bitrates, etc.) only further underlines my point of how broken weak metadata is.

[curiousuburb]

MPEG7 (http://en.wikipedia.org/wiki/Mpeg7), as a metadata schema, extends MPEG4 with elements beyond codec and copyright... right down to phoneme and picture region.

This presents interesting possibilities for meta-tagging colours/shapes prior to inter or intra-frame compression, and the potential to allow optizimations post-facto (like tweaking the EXIF in PShop to alter the exposure of a digicam pic rather than editing the image pixels).

Accurately tagging schema elements to that level of granularity is the killer, although there's some interesting AI-supported stuff out there... IBM "Marvel (http://mp7.watson.ibm.com/marvel/)", etc.

But I didn't want to go too far off on a tangent that we get a bidding war...

I'll see your MPEG7 (http://www.chiariglione.org/mpeg/standards/mpeg-7/mpeg-7.htm) and raise you MPEG10 ;)