[mythtv] [mythtv-commits] Ticket #1608: Proper Handling of Alsa AC3-PassThru

Markus Schulz msc at antzsystem.de
Sun Apr 2 01:42:02 UTC 2006

Am Sonntag, 2. April 2006 02:31 schrieb Martin Ebourne:
> On Sat, 01 Apr 2006 16:17:05 +0200, Markus Schulz wrote:
> > What have you configured as alsa output? ALSA:spdif? or similar
> > alias?
> No, I have AudioOutputDevice configured as 'ALSA:hw:1' which is
> direct to the hardware.

This means only that you are using soundcard 1. nothing more. All other 
is controled from alsa (incl. asoundrc)

> > IIrc the iec958 is used all the time if you pass thru, cause iec958
> > is the sample format for sp/dif output. Check "aplay -L" for all
> > pcm-output device strings.
> No, my soundcard does not need iec958, it always sends all PCM sent
> to it out through the s/pdif. Even in alsamixer there's only one

can i please see a "aplay -l" and "aplay -L" from your card?
I can't imagine how a soundcard can pass thru uncompressed and 
compressed data to sp/dif without setting the the correct channel 
status bit (for the compressed IEC61937 datastream).
Cause, the receiver on the other side must detect if he can play the 
data directly (uncompressed pcm) or must decode it. (AES0 0x02 means 
exatly this). 

> > Best way will be
> > an additional input field (next to passthru checkbox) where you can
> > enter the alsa-pcm-device string for ac3 streams differently to
> > uncompressed pcm data.
> I think this is the best solution. There appear to be several
> different ways that s/pdif and passthru are implemented in ALSA, and
> a good many more variations in people's setups, so I'm rapidly coming
> to the conclusion that the only way to satisfy everyone is to make
> both configurable independently.

but can you please test my patch with your hardware if you change the 
iec958 Options String to: "iec958:{CARD 1 ..."

Markus Schulz

A: Because it breaks the logical sequence of discussion
Q: Why is top posting bad?

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