For a more generic overview of TV audio-over-PCI, including other (non-bttv) analog cards, see PCI TV audio
btaudio is a kernel module for reading the audio directly from Brook Tree bttv supported TV-cards. This may or may not work on your TV-card depending on chipset and used features by the card manufacturer. Give it a try if you want.
btaudio provides an OSS interface. For an ALSA driver, see snd-bt87x. In Debian (2006-02-14) this module is used automagically and the following is unecessary.
This is for Gentoo, so this will be a little strange to some. :)
To get btaudio working with ATI TV Wonder, put the following lines into /etc/modules.d/bttv.
alias sound-slot-1 btaudio alias sound-service-1-0 btaudio
Also add btaudio to /etc/modules.autoload/kernel-2.6.
For a Fedora setup add the following lines to /etc/modules.conf.
alias sound-slot-1 btaudio alias sound-service-1-0 btaudio pre-install btaudio modprobe via82cxxx_audio
The pre-install line makes sure that the sound card driver is loaded before the btaudio, so that btaudio will always get /dev/dsp1 and /dev/dsp2.
Also load the btaudio module from the /etc/rc.d/rc.local file with the following command.
In MythTV, setup your device /dev/video0 with /dev/dsp1 for the sound, and it might just work!
For auto-loading by Alsa, you can do the following:
alias snd-btaudio btaudio alias sound-slot-1 snd-btaudio alias sound-service-1-0 snd-btaudio
Alsa basically just looks for anything beginning with "snd-", and nobody really wants to load btaudio using rc.local. This works great and gives status on boot-up through Alsa.