[mythtv] [mythtv-commits] Ticket #1104: multi channelaudio support

[Michael T. Dean]

On 08/16/2006 03:33 PM, Jan Kleinig wrote:

> Hi,
>
> I have the same effect with AC3 using ALSA:surround51 :( But using 
> this device, I have even no sound playing a non-AC3-recording :(


Right.  That was the, "For now," in the request.  :)  BTW, which sound 
card are you using?

Mike

>
> Michael T. Dean schrieb:
>
>>On 08/15/2006 12:33 AM, Mark Spieth wrote:
>>
>>  
>>
>>>>Analog and ac3, don't know about german channels providing dts ;)
>>>>   
>>>>
>>>>      
>>>>
>>>the 6 analog channels out (for me) are
>>>L,R        -> audio out plug 1
>>>C,LFE    -> plug 2
>>>SR,SL    -> plug 3
>>>
>>>afaict this is standard.
>>>will do some testing over the weekend or earlier if I have time with my 
>>>limited setup.
>>>
>>>does your channel have 6ch audio? (including LFE/subwoofer)
>>>can you get the startup part of the frontend log to see what the audio part 
>>>is doing.
>>>
>>>    
>>>
>>
>>The "standard" in ALSA is described in the comments in 
>>/usr/share/alsa/pcm/surround*.conf .  The standard for 7.1 audio is:
>>
>>#  Hardware output from 7.1 speakers
>>#  Samples must be positioned:
>>#    chn0 - front left
>>#    chn1 - front right
>>#    chn2 - rear left
>>#    chn3 - rear right
>>#    chn4 - center
>>#    chn5 - lfe
>>#    chn6 - side left
>>#    chn7 - side right
>>
>>And 5.1 is the same but without channels 6 and 7.  (Channels 6 and 7 are 
>>incorrectly labeled 7 and 8 in the comment.)
>>
>>However, some hardware doesn't use this standard.  For that hardware, 
>>different configurations are specified using a translation table 
>>(ttable) in the "standard" surround device aliases (i.e. surround40, 
>>surround51, surround71, etc.) in /usr/share/alsa/cards/*.conf .  
>>Therefore if using non-standard hardware /AND/ using an ALSA built-in 
>>device alias, your non-standard hardware will react as would standard 
>>hardware.
>>
>>Specifically, the ICE1724, ICH, ICH4, NFORCE, and VIA8237 all use 
>>non-standard channel-output mapping for surround.  (So, Mark, if your 
>>"standard" is based off one of these cards hardware usages, it's not the 
>>real standard.)
>>
>>Anyone using a custom definition for his/her audio could add a 
>>translation table to the custom device alias in /etc/asound.conf or 
>>~/.asoundrc.  Asking the users to learn enough about ALSA to do so may 
>>be more than we should expect, though.  (See 
>>http://www.gossamer-threads.com/lists/mythtv/users/134552#134552 for 
>>more on ttable.)  Unfortunately, that means the only way to know for 
>>sure which mapping the hardware uses is to parse the 
>>/usr/share/alsa/cards/*.conf files, but the only way to know if we 
>>should use the hardware mapping (instead of ALSA default) is to also 
>>parse the /etc/asound.conf or ~/.asoundrc and to find out whether the 
>>device alias specified to Myth is an ALSA built-in or a redefined custom 
>>version of the ALSA built-in or a custom alias that slaves to one of the 
>>ALSA built-ins or a custom alias that provides its own translation 
>>table.  Obviously, none of this should be done by Myth...
>>
>>For now, Jan, what happens when you change your MythTV audio output 
>>device to "ALSA:surround51"?  With that, you'll be using an ALSA 
>>built-in alias, so you'll get the ALSA-standard mapping, so if Mark used 
>>the ALSA standard for the patch, you should get proper output to the 
>>proper speakers (assuming your speakers are connected to the correct 
>>outputs ;).
>>
>>Mike
>>_______________________________________________
>>mythtv-dev mailing list
>>mythtv-dev at mythtv.org
>>http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-dev
>>
>>
>>  
>>
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