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laptop and desktop

Posted Sep 22, 2008 0:01 UTC (Mon) by mezcalero (subscriber, #45103)
In reply to: laptop and desktop by nim-nim
Parent article: LPC: Linux audio: it's a mess

Uh? PA supports surround sound just fine. Even does automatic upmixing/downmixing from/to stereo for you.

Also, I don't "dismiss" JACK and the community around it. It's great stuff. But solves a different problem as PA. That's all.

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laptop and desktop

Posted Sep 23, 2008 5:04 UTC (Tue) by foom (subscriber, #14868) [Link]

> Uh? PA supports surround sound just fine. Even does automatic upmixing/downmixing
> from/to stereo for you.

Sure, but doesn't transparently support the most common source/sink of surround sound: AC3
DVD audio to AC3 over SPDIF output.

If PA automatically supported AC3 encoding of surround sound to my SPDIF output, without
having to manually configure an external encoder program, that'd be good.

If PA could allow routing of AC3 audio through to the SPDIF port without the decoding/encoding
overhead and resultant quality degredation, that'd be great.

But, if it could do that, *and* transparently fall-over to doing a decode/mix/encode when it
needs to mix another stream into the output (e.g. an alert sound or what have you), it would be
an absolutely amazing achievement: that's something that you just can't do today. And I'd really
like to be able to do that.

Also, volume control is an interesting trick when not decoding the ac3 stream locally; I dunno
much about it, but I'm led to understand there's some metadata in the frames which can be set to
affect the volume on the decoder. Maybe (hand-wave) that could be modified in-flight without
re-encoding the stream. :) If PA could do that, that'd be even another advantage over the
existing ALSA solution.

One can always dream...

laptop and desktop

Posted Sep 23, 2008 13:45 UTC (Tue) by mezcalero (subscriber, #45103) [Link]

PA focuses on PCM right now. Support for pass-thru codecs is on our TODO list.

However, please note that we will probably never support on-the-fly AC3 decoding or encoding due to patents.

Lennart

laptop and desktop

Posted Sep 23, 2008 14:52 UTC (Tue) by foom (subscriber, #14868) [Link]

Sad to hear that about the patents...but is there really any issue with using an AC3 encoder/decoder library if the user happens to have one installed already? (maybe they've already paid the licensing fee to Dolby, e.g. through buying a Dell with Ubuntu preinstalled).

laptop and desktop

Posted Sep 23, 2008 20:07 UTC (Tue) by mezcalero (subscriber, #45103) [Link]

I am happy to merge patches for that.