No playback of AC3 m4v's in Quicktime X - problem?

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juicybiscuit
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No playback of AC3 m4v's in Quicktime X - problem?

Postby juicybiscuit » Sat Aug 22, 2009 11:43 am

Hi there. Just trying out a build of Snow Leopard and Quicktime X.

Quicktime X can't seem to open any of my m4v's that have ac3 audio. Guessing it may be a Perian a52codec.component thing?

Any ideas?

ctalibard
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Re: No playback of AC3 m4v's in Quicktime X - problem?

Postby ctalibard » Mon Aug 24, 2009 6:26 pm

I have the same problem, using build 10A432 which is meant to be the gold master that being release on Friday. Videos created using Handbrake with identical settings except audio codec. AAC stereo works in QT X, but if AC3 is the only audio I have to play them in QT 7 instead.

For AAC-based movies, reported Movie Inspector formats differ between the two versions of QT though:
QT X: H.264, 656x572, Millions, AAC, 2 channles, 48000 Hz
QT 7: JVT/AVC Coding, 656 x 572 (933 x 572), Millions, AAC, Stereo (L R), 48.000 kHz

EDIT: I now understand that Perian was never used for m4vs. So the above is a bit of a red herring. Investigating more.

ctalibard
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Re: No playback of AC3 m4v's in Quicktime X - problem?

Postby ctalibard » Tue Aug 25, 2009 5:15 am

As far as I can tell, it is A52codec not being recognised. removing Perian completely and manually reinstalling just the a52codec allows QT7 to work just as before but not QTX

ctalibard
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Re: No playback of AC3 m4v's in Quicktime X - problem?

Postby ctalibard » Tue Sep 01, 2009 6:55 pm

I posted this on another topic, but it's also relevant here too. So for completeness:

It's a QT X problem.

I think it's worth clarifying the difference between Quicktime, and Quicktime Player. The latter being an application that uses the former to play and record videos. Also rather confusingly, even if you didn't install Quicktime 7 from the optional installs, you still got it because it's essential for SL to work properly. The optional install really should have been called Quicktime Player 7.

QT X has no plugin capability, support for only a few modern codecs, and no basic editing ability. So, in Quicktime Player X, operations (like trimming) and containers (like mkv) not supported by the QTX infrastructure are delegate to a separate 32-bit QT 7 based process which decodes and returns the data. This is why certain videos that require Perian seem to work in Quicktime X. The truth of the matter is that they work in Quicktime Player X, and are being handled under-the-hood by the QT 7 infrastructure.

The problem with m4v's seems to me to be that QT X thinks it can handle that container, and when it can't (because it's got AC3 audio) it fails to delegate the handling of it to QT 7.

Trevize
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Re: No playback of AC3 m4v's in Quicktime X - problem?

Postby Trevize » Wed Sep 02, 2009 9:43 am

Actually, QuickTime X can reproduce ac3 from mp4/m4v if you have a 64bit version of a52codec, or if you start qtx in 32bit mode. But only if you have only one ac3 track and no other audio track.

ctalibard
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Re: No playback of AC3 m4v's in Quicktime X - problem?

Postby ctalibard » Wed Sep 02, 2009 9:54 am

Actually, that makes perfect sense, because the A52Codec is a Core Audio plugin, not a Quicktime one IIRC.

ctalibard
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Re: No playback of AC3 m4v's in Quicktime X - problem?

Postby ctalibard » Thu Sep 03, 2009 6:05 pm

Opening QT Player X in 32-bit mode allows AC3 audio to work just as you describe. Still no AC3 passthrough though. Works on Perian handled containers, but not on m4vs :sad:

Thargok
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Re: No playback of AC3 m4v's in Quicktime X - problem?

Postby Thargok » Fri Sep 04, 2009 1:07 am

There will likely never be a fix to this. I don't know who forces AC3 audio into a .mp4 container, but violating specs typically results in problems like this. (Like trying to drive a car underwater)

As I have never seen a file like this, I speculate that renaming the file to represent a QT container (.mov) will likely allow it to play do the the fact that the MPEG-4 container is practically a Quicktime container.

Trevize
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Re: No playback of AC3 m4v's in Quicktime X - problem?

Postby Trevize » Fri Sep 04, 2009 6:22 am

Violating what specs? Apple made their own mp4 brands, and the way to store ac-3 inside the iso file format has been described by ETSI and approved by the MP4 Registration Authority: http://www.mp4ra.org/codecs.html

But still, Apple doesn't really care about ac3 outside of the appletv.

raytw
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Re: No playback of AC3 m4v's in Quicktime X - problem?

Postby raytw » Sun Sep 06, 2009 10:52 am

Trevize is absolutely right, although putting AC3 sound into an m4v container is a pretty new idea (sometime early in 2008, I believe), so many people still think it's non-standard. However, it's odd that QuickTime X objects to files containing other audio tracks, as the Apple TV, at one stage, wouldn't accept m4vs containing AC3 audio UNLESS they also contained an AAC track. Apple was (and possibly still is) reluctant to accept the idea of m4vs containing AC3 tracks, since the latter is an old form of audio coding. The fact remains, however, that there is a huge amount of material that has AC3-encoded sound and transcoding it to an alternative format would be unnecessary and would result in a degradation of sound quality.


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