[mythtv-users] Dolby 5.1 SPDIF Passthrough Audio

[Michael T. Dean]

On 07/22/06 00:40, Brandon Rogers wrote:

>            I have had my mythbox (2.8 GHz HT Pentium 4, pcHDTV 3000,
>optical 5.1 passthrough audio) running for some time and have found a few
>quirks that I wonder if anyone has come across and possibly a solution.
>
>-          My sound is being passed through to an external surround sound
>receiver.  When 5.1 audio is sent to the receiver, the sound is not
>immediately detected as 5.1 audio (no sound at all until I switch back and
>forth a few times between inputs and eventually 5.1 will come on).  After
>the 5.1 sound comes on, the audio is perfect, without problems, until a
>commercial comes on without 5.1 audio or something of the like.  Then the
>switching process has to re-done until the sound is detected as Dolby
>Digital 5.1.  The sound is connected via optical SPDIF.  Non-"Dolby Digital
>5.1" signals come of the wire without a problem.  When a hardware DVD player
>is connected to the receiver, the surround sound is immediately detected and
>there are no problems.  Does anyone know of a problem of ALSA / MythTV to
>properly "alert" the receiver of incoming 5.1 signals?  Any one else have
>any ideas what this could be and why this could be happening?
>

Yes.  Myth doesn't fully configure AC-3/DTS output before sending to the 
receiver.  The problem is known, but we haven't yet created a solution 
that works for all sound card/receiver combos ( 
http://www.gossamer-threads.com/lists/mythtv/users/199201#199201 ).  
There have been a couple of patches posted, but they've all been "hacks" 
that work for only specific combinations.

Your choices for now include fixing it yourself (or at least hacking 
your version for your card/receiver) or forcing your receiver to switch 
to AC-3 decoding.  (Does your receiver have a button to force the mode 
instead of just switching inputs back and forth until it figures it out?)

#1598 - http://www.gossamer-threads.com/lists/mythtv/commits/193725#193725
discussion - http://www.gossamer-threads.com/lists/mythtv/dev/209110#209110
discussion - http://www.gossamer-threads.com/lists/mythtv/dev/206535#206535


#1608 - http://www.gossamer-threads.com/lists/mythtv/commits/194162#194162
discussion - http://www.gossamer-threads.com/lists/mythtv/dev/194225#194225

Mike