[mythtv-users] [Fwd: Using JACK for Audio - SOLVED]

Martin Lynch martin.lynch at shaw.ca
Tue Jan 8 13:42:25 UTC 2008

> -------- Original Message --------
> Subject: 	Using JACK for Audio
> Date: 	Mon, 07 Jan 2008 01:03:45 -0800
> From: 	Martin Lynch <martin.lynch at shaw.ca>
> Reply-To: 	martin.lynch at shaw.ca
> To: 	mythtv-users at mythtv.org
> Has anyone successfully used JACK to output audio from MythTV? I start 
> qjackctl, select JACK from the front end settings in Myth, then tune 
> in a channel. The connection shows ever so briefly in qjackctl's 
> connections box but then disappears. I use JACK successfully day in 
> and day out for music recording projects (with Ardour) without any 
> problems whatsoever, so I don't think it's on JACK's end. I also tried 
> selecting various sample rates (by default I use 96K but tried it with 
> 44.1K and 48K) and with and without real time priorities, all to no 
> avail. I scoured the web with no luck; also all my old archives of 
> this list and the only matches I got were in the context of "I don't 
> know jack about..." - nothing relating to JACK... Anyone have any 
> suggestions?

Few things I had to do to get JACK to work:

- In the General section of Setup in the frontend, I had to change 
"JACK:output" to "JACK:" This finally allowed me to connect to JACK, but 
the audio was horrible - slow and distorted and goofy.
- I changed some settings in JACK: changed sample rate to 44.1 (from 96) 
and changed the frames/period to 256 (from 64). Periods/buffer remained 
at 3. The latency, which I ordinarily keep at 2ms for music projects 
went up to 17.4ms (ie. (256 X 3)/44,100). Real time checkbox remains 
checked in JACK, and I'm using "Extra Audio Sound" in Myth.

This works great and has eliminated audio choppiness on HD channels 
which had recently developed and which slowed down playback.

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