[mythtv] [mythtv-commits] Ticket #1104: multi channelaudio support
Michael T. Dean
mtdean at thirdcontact.com
Wed Aug 16 22:19:06 UTC 2006
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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