Where's real AC3 Passthrough on the Mac?

Posted by Thoughts and Ramblings on Friday, March 14, 2008

In my previous post, I discussed how to do AC3 passthrough using Perian. Unfortunately, this method is really a hack, and doesn’t work in all situations. There is a better solution though.

Apple has enabled AC3 passthrough with Quicktime. They have enabled it on the AppleTV to support playback of their HD movies. The code for passthrough is even in the latest version of Quicktime on the desktop, but the celebration ends there. Apple has not exposed a method for enabling passthrough on the desktop either through the user interface, or a hidden preference. They have not even exposed a method for developers to use it through Quicktime (I’ve tried).

So, what is to be done about it? Tell Apple to address this. Go to http://bugreport.apple.com and fill in an enhancement request. You can reference my report id, which is 5799133, and says:

Please enable a method for AC3 passthrough on the desktop using Quicktime. There are no licensing issues for passthrough, and you already have the enabling code in place. The AppleTV proves that your code works, so please add the interface so this can be used on the desktop.

The hack in use by Perian isn’t perfect. It does not work with all receivers where the true passthrough will. Audio outputted using the encoded digital audio output of the optical interface works, as evident by the DVD player, but this method is not available to Quicktime in any documented manner.

If enough people fill in reports, Apple should realize this is important to people and enable the interface. Please use your own words in your own reports; it says more to them if the reports are not copy/paste.

Update: Apple has marked my ticket as a duplicate of 4557501.

Legacy Comments:

fatez - Mar 20, 2008

Hey, Any news for the real AC3 passthrough ?

Graham Booker - Mar 20, 2008

No more that what I have stated here. Bug Apple about it. If you look at the assembly code, you can see that much of the AC3 passthrough code is in the latest Quicktime, but any method of calling it is disabled.

Ignignokt - Apr 3, 2008

It appears that Apple’s latest version of Quicktime, 7.4.5, completely breaks Perian’s AC-3 passthrough. I had a working setup where I could play files in Quicktime, iTunes, or Front Row with AC-3. After the update, none of it works. (And now iTunes crashes with a bus error any time I add or modify a file. Reverting to an earlier version of Quicktime and iTunes doesn’t fix it. Great QA, Apple!) OSXBMC seems to have a pretty decent AC-3 and DTS passthrough that’s unaffected, and it’s open-source and appears to use liba52 as well. Perhaps it would be worth taking a peek at their method?

Graham Booker - Apr 3, 2008

Ignignokt, No, they didn’t break it. It still works. I know how OSXBMC does passthrough, as well as VLC. I know exactly what they are doing, and I have submitted several requests to apple to enable what is needed. They haven’t responded except to say that it would be nice, hence the entire reason for this blog post.

Ignignokt - Apr 3, 2008

Well, that’s even more frustrating to hear! :-P Something must be seriously borked after my update then, because no amount of reinstalling, re-updating, restarting, and resetting various prefs for iTunes, Front Row, Perian, and a52 has fixed anything. I’m left with a total reinstall to get my mini HTPC back up and running…. I do appreciate all the great work you’ve done. Here’s hoping Apple listens to you (and me, and everyone else who’s submitted this bug) in the next Quicktime update!

Graham Booker - Apr 4, 2008

Keep bugging Apple about it. I sincerely hope that they realize sales depend on this. I already know at least one sale that is waiting on this to be resolved, otherwise he’ll purchase a PC and be done with it.

emd - Apr 7, 2009

Well, Apple enabled HD rentals on the desktop…have we any hope?

hot videos - Apr 7, 2011

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Graham Booker - Apr 10, 2009

emd, I don’t know much about the rentals since I’ve never rented anything from iTunes (too expensive). I expect it is easy if the DRM is first broken. Otherwise, the only solution is to bug Apple about it: http://bugreporter.apple.com

David - Apr 12, 2008

I filed a bug report too. My report id is 5860429.

James - Apr 18, 2008

Also filed a bug report. Bug ID# 5872543

Nick Vance - Apr 18, 2008

What a bummer they broke this again. It was working so well… Now I can’t play the audio in all the files that I ripped with AC3 in Handbrake on my computer even though they play great from my AppleTV (I don’t understand why VLC doesn’t recognize the encoded audio stream correctly). Here’s hoping for a fix soon… Maybe someone can find a security hole in QuickTime so they hurry up and push out a new version. Hehe.

endlessruin - Apr 18, 2008

This is really disappointing. You would think that Apple would just take care of this, it doesn’t seem too difficult to fix. I wonder if they aren’t fixing to make htpc people buy an apple tv instead. I can’t see any rationale for it otherwise.

toxlab - Apr 19, 2008

To get AC3 passthrough working again use Pacifist to reinstall quicktime 7.4.1 from its package. Pacifist allows you to reinstall older versions over newer versions. Then reinstall Perian 1.1. You can leave the updated FR and iTunes, they work fine with the QT 7.4.1

Tumbles - May 3, 2008

Great work Graham and Toxic for your advice in this area. I’ve followed your posts on a few forums. This is one of those crazy things that I just can’t believe Apple doesn’t sort. The not doing it so people buy apple tv’s is potentially one answer, although I thought AppleTV just put out pro logic anyway, not proper passthrough. Another theory I have is that Apple considers that 95% of people wanting to passthrough AC3 from MP4/MKV etc at the moment are doing so in order to play ripped DVD’s which is obviously a copyright issue. So they are basically saying we’re not going to write code helping you to break copyrights. But with iTunes movies gaining speed, they have written the code ready for a future version of Quicktime when they feel its in demand enough in support of legit downloaded movies, and then they’ll tout it as some big new feature.

Graham Booker - May 3, 2008

First, ripping DVDs is not a violation of international copyright law, as long as it is not distributed to others. Ripping a DVD for your own use is no different than ripping a CD for your own use. Both fall under fair use. The issue is that ripping a DVD in the US is now a violation of the DMCA. As is typical of a lousy president, instead of enforcing laws already on the books, create more laws which accomplish nothing more than to restrict the freedoms of law abiding citizens. Passing a law against already illegal action isn’t going to stop any of it. Apple has admitted to me that they are not interested in enabling ripping of DVDs in any form, as they have too many relationships with studios. The only way I see Apple enabling AC3 passthrough on the desktop is if they eventually enable HD rentals on the desktop.

Nick Vance - May 3, 2008

I’m pretty sure the loss of AC3 passthrough in the latest versions of QuickTime is a bug. Apple certainly doesn’t care if you’re passing through stereo or AC3 audio from your own computer. Indeed they still let you pass through AC3 audio from the DVD player application which is perfectly capable of playing ripped Video_TS files. Certainly there would be more of an incentive to fix this if they did HD rentals with AAC support on the desktop however. Also @Tumbles (comment 12): the AppleTV Take 2 *does* support AC3 passthrough (not just ProLogic II). Apple explicitly supports this on their HD movie rentals.

David Hampson - Jun 5, 2008

This is just a thought, but when we are using ac3 passthrough, then all other system sounds need to be diverted and/or blocked. This is very un-Appleâ„¢ like. This means that we won’t be alerted to an iCal alarm, iChat request, incoming mail, etc. ATV does not have to worry about these things, so it enabled passthrough. Apple inc. is very resistant to doing un-Apple like things, we may want to change strategies in getting Apple to open this up. –Dave

Graham Booker - Jun 5, 2008

Dave, Except, they’ve already done this with the DVD player for years; so there’s no excuse. They know how to do it, and QT is no different.

Josh T. - Jun 8, 2008

This worked great, used Pacifist to downgrade to 7.4.1 and all is well…

Josh T. - Jun 8, 2008

(Let me preface this by saying that I just got all this up and running so the fact that I got the AC3 passing through last night was a major step.) The problem I’m having now is that the only way that the AC3 comes through in Front Row is if it is the only audio track on the encode. If I encode a file with HB and choose AAC + AC3 it ALWAYS plays the AAC track. I’ve compiled the latest HB and even put track 1 as AC3 passthrough only and then track 2 as AAC hoping that Front Row would automatically go for track 1, no dice still defaults to AAC with no way that I know to switch it. Obviously I could encode them as AC3 only, but then that only allows them to be played in our living room since no other room we have has Dolby Digital. Anyone have a solution for this?

Graham Booker - Jun 8, 2008

Josh, This is not a support forum, nor will I allow it to be so. Don’t ask for help here! Perhaps you should read the pre-existing documentation and tell Apple to get over their stupidity and do something right for a change.

Graham Booker - Jun 23, 2008

Reporting bugs only requires a (free) Apple ID. If Apple ignores a requested feature for this long, our only hope is that they pay attention to the volume of requests.

Crispin - Jun 23, 2008

Why does Apple break my heart every time I am about to buy a Mac? They seem to miss the mark when I need to address advance features. Features that just work, without drama, in the Windows hardware/software environment. Even more heartbreaking, since I don’t have an ADC membership I cannot report the issue. Mac Pro purchase, pending. Foiled again.

Chris H - Jun 25, 2010

I have filed report 8131881 with Apple.

Rakor - Jul 12, 2008

Heyho! Is the new QT doing the AC3-passthrough? I really need to do an update because of iPhone2.0 but I don’t like to get trouble with my AC3 again…

Nick Vance - Jul 24, 2008

Sebastian: the static noise from the .m4v file is the bug we’re talking about. The reason .mkv works is because it’s supported through Perian which doesn’t have the bug. I don’t want to use .mkv for my videos as it’s a poorly supported format on the Mac… and plays terribly on the AppleTV (where I watch most of my movies).

Sebastian - Jul 24, 2008

OK Nick, than the right solution is to rip my DVDs to .mkv, import it into quicktime and save it to .mov, so it can be played with frontrow w/o problems. At least until that bug (if it is a bug and not a feature :D) is fixed. That should work for your AppleTV, too. If anyone wants to take a look at this: http://discussions.apple.com/thread.jspa?threadID=1627107, that would be helpful.

Sebastian - Jul 23, 2008

Hi all! I am using Leopard with all updates (QT 7.5) and the AC3-Hack works fine (Quicktime and VLC work with AC3 passthrough). @Graham: I converted one of my DVDs with Handbrake 0.92 one time to m4v and one time to mkv, both times using H.264 for video and AC3-Passthrough for audio. the .mkv works in quicktime, with the .m4v I get static noise instead of sound. Movie Info from Quicktime says for the m4v [AC3, 5.1 (L C R Ls Rs LFE), 48,000kHz] and for the .mkv [AC3, 5.1 (L R C LFE Ls Rs), 48,000kHz]. Does that make a difference or is that the broken code you wrote about? I can save the .mkv as .mov and that file works without flaws.

Jerome - Oct 24, 2009

Works dandy in Leopard on my mini. Now getting 5.1 from mkvs through to my Onkyo 807. Thanks a great deal, sir.

Nick Vance - Jul 26, 2008

Sebastian: the point is to have one file that plays correctly with AC3 audio on the Mac and the AppleTV. Your solution does not fix that, because when you save it as a .mov you get (A) a second file and (B) that file will have the same problems with digital static as the first (or it would be in surround sound anymore; check your files if you don’t belive me). My best current solution is to rip your DVD in HandBrake using the default AppleTV settings. This encodes a file with both AAC Dolby Pro Logic II and AC3 Dolby Digital sound. The AC3 Digital track will play correctly on your AppleTV (assuming you have it set up correctly to play digital audo and AC3 passthough) and will play on your Mac once Apple fixes the QuickTime bug (or if you revert to a pre-bug version of QuickTime). In the meantime, your Mac will correctly play the AAC Dolby Pro Logic II track for stereo sound (perhaps enhanced to 4.1 if you have a Pro Logic II decoder on your speakers).