[mythtv] Fwd: iec958 output (not passthrough) with Alsa rate pluginproblem
lef at freil.com
Tue Jan 16 00:30:35 UTC 2007
On Jan 15 2007, John P Poet wrote:
>On 1/15/07, Mark Spieth <mark at dclabs.com.au> wrote:
>> > Hello,
>> > I have discovered a little problem with MythTV and audio output. For
>> > output I'm using the passthrough feature to the iec958 device to a
>> > surround
>> > sound reciever. This works fine, however when the audio is not ac3 I
>> > want the output to go to iec958. I have created a rate plugin pcm
>> > for alsa to change the rate from 44.1 to the 48Kz required by the
>> > output device and then set the non-passthrough device to ALSA:hq48k.
>> is this feature desirable? if so Ill add it to the multichannel audio
>Why not do the rate conversion in your .asoundrc file?
> Not all sound cards require 48KHz. For example, sound cards based on the
> Envy24 chip will pass through 44.1KHz just fine. The reason I have a
> Envy24 card in my frontend, instead of using the onboard sound, is to get
> 44.1KHzwithout any kind of conversion.
>MythMusic sounds *MUCH* better (to my ears) with my Envy24 based card
>compared to my old SB Live! I attribute this to it's ability to pass
>through 44.1KHz without having to resample.
>I believe I read that Intel's new HD audio spec also will pass through
>44.1KHz without needing it converted to 48KHz.
Not having the rate conversion would certianly be desirable, however it is
not possible for everyone. In my case I am using the .asoundrc and the alsa
rate plugin to create a high quality rate conversion and the sound is very
This is easy enough to do, that providing instructions on how to setup in
the wiki is probably sufficient. If there were a way to determine by
probing the hardware that a rate conversion was required then I would
recommend it being automatic and in myth, however there are also other
reasons beyond rate to setup local pcm's. I wouldn't mind updating the
wiking on this as soon as he flow control issue is solved. Now if I could
just figure out how to get alsa to map a OSS emulated /dev/pcm to an
arbrary plugin pcm instead of just mapping to hardware pcms. Some of the
software still likes to use oss devices.
lef at freil.com
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