AC3 Passthrough Compatibility Matrix

Posted by Thoughts and Ramblings on Monday, June 9, 2008

Since some parts of AC3 passthrough work, and others do not, I decided to create a bit of a compatibility matrix to summarize it. I’ve added the related bug id’s I’ve reported, which have gone unanswered, in parentheses.

The latest version of perian (to be released soon), will choose between using the hack method for passthrough, and Apple’s method. Anywhere labeled “Hack” will never work with Apple’s method, so it is bypassed to avoid their broken code. The hack does not work with all 5.1 receivers. Taking a file format which is not properly framed, and making it into a .mov file will not correct the framing. Likewise, it will not destroy the framing of a properly framed file format.


File Format Properly Framed Improperly Framed
.mov Will Passthrough Silence (5876598, 5994328)
.mkv Will Passthrough *1 N/A
.avi N/A Hack (5876598)

Note: I have never seen properly framed avi files, nor improperly framed mkv files.
*1: MKV files will passthrough if the import is allowed to complete. I tested this by making a reference movie out of the mkv file. If the import does not complete, this will result in silence.


As far as I know, the hack always works, and real passthrough does not, in all cases. See related post.

Legacy Comments:

MichaelLAX - Jun 10, 2008

Looking forward to your observations on QT 7.5

Push Eject - Jun 18, 2008

As always, thanks for your persistance with this, Graham.

Erik - Aug 12, 2008

thank you very much for your blog, Graham.. It has helped me a lot with my macbook setup… I am probably asking for too much.. but is there a way to specify passthrough for only certain outputs? I hate going to terminal and audio midi setup everytime I change the output… even tried automator to do it for me, with no luck.. So far, I`ll just stick with vlc.. thanks again, keep up the good work! Erik

Graham Booker - Aug 12, 2008

Erik, It could theoretically be possible; but non-trivial. Maybe in the future.