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

[Jan Kleinig]

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 :(

-Jan

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
>
>
>   
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://mythtv.org/pipermail/mythtv-dev/attachments/20060816/97dc0c52/attachment.htm