[alsa-devel] Status of Dolby Digital on-the-fly encoding? (via a52 plugin)

Takashi Iwai tiwai at suse.de
Mon Dec 17 11:30:56 CET 2007

At Tue, 11 Dec 2007 14:22:49 +0100,
Dr. Alexander K. Seewald wrote:
> I am trying to output Dolby Digital data via coaxial cable to the
> Logitech Z-5450 5.1 speaker set. Presumably, a52 is the right plugin
> for this, taking six channels and combining them into the right
> format. However, I cannot seem to make the Z-5450 understand the
> format... it always displays "No digital data" and does not output
> anything.
> Now, the documentation is very sparse on this, but states that
> Dolby Digital is supported, as well as DTS and DTS with 96kHz
> sampling rate and 24bit samples. The Z-5450 can play digital PCM
> stereo data, but this only activates left and right speaker (it is
> possible to set an effect to distribute sound to the other speakers,
> but this is insufficient for my purpose). I can play digital DVD
> 5.1 sound by attaching the coaxial cable to a DVD player.
> As of now, speakertest -c 6 tries to play sound on all speakers, but
> only left and right respond. For all other speakers, "No digital data"
> is displayed on the Z-5450 console. This is consistent with the Z-5450
> not able to play six-channel PCM data. However, using -Dplug:a52 and
> .asoundrc =
> pcm.a52 {
>   type a52
> }
> (with various settings)
> always shows "No digital data" and no sound output. I had a sample
> DTS 96/24 file a while ago which was able to activate all speakers,
> so the data connection is ok. But sadly I have misplaced it; in any
> case DTS 96/24 support is not what I'd expect in the near future.
> Has anyone successfully output Dolby Digital (A52, AC3, ..) data via
> coax to the Z-5450 or a similar model? I'm using the newest alsa
> drivers and plugins on an 2.6.11, and the stereo-PCM output has been
> working for years... but this one keeps bugging me.

Check first whether "ac3dec -C foo.ac3" work to send AC3 data (not on
the fly encoding).  Try a52 plugin after confirming this works.

(And, I know there are still some bugs with a52 plugin but no time to
 play with it right now...)


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