View source for PCI TV audio

If your analog TV capture card doesn't support a physical connection to the soundcard, (either through an internal connector or an external jack), or if you just don't want to use that connection, most cards supported by v4l2 allow you read the audio directly from the card using the ALSA sound system.


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== BTTV ==

The following kernel modules support capturing digitized audio directly from the bttv based cards.

* [[snd-bt87x]] - ALSA driver
* [[btaudio]] - OSS driver

If you are unsure of which one to use, you probably want the ALSA driver.  ALSA in the Advanced Linux Sound Architecture and is the default sound subsystem for Linux, starting with version 2.6.0.  ALSA also supports OSS emulation for those applications that require it.

----

== SAA7134 ==

For all '''saa7134''' cards, you can load '''''saa7134-alsa''''' (from kernel 2.6.15 on), and it'll give you a sound device you can use with Myth. The number of the device can be found at ''/proc/asound/cards'', for example:

<pre>
# cat /proc/asound/cards
 0 [IXP            ]: ATIIXP - ATI IXP
                      ATI IXP rev 1 with AD1888 at 0xfe800000, irq 18
 1 [SAA7134        ]: SAA7134 - SAA7134
                      saa7133[0] at 0xfdf00000 irq 18
</pre>

here, the SAA7134 took device 1. You can use /dev/dsp1 as the audio device for this capture card, and it should just work. If it doesn't, try fiddling with it's controls by running ''alsamixer -c 1'' (or the number your card got). Pushing all volume knobs to the max and setting "Capture" on all of them usually helps. For saa7134, the audiorate must be set to 32000.


----

== CX88 ==


For most '''cx88xx''' cards, the '''''cx88-alsa''''' module does the same as saa7134-alsa. Some (cheaper) cx88 cards don't support PCI audio, though... Again:

<pre>
# cat /proc/asound/cards
 0 [SI7012         ]: ICH - SiS SI7012
                      SiS SI7012 with ALC655 at 0xf400, irq 20
 1 [CX8811         ]: CX88x - Conexant CX8811
                      Conexant CX8811 at 0xfa000000
</pre>

You should get a card at ''/proc/asound/cards'' after loading cx88-alsa. If you don't, you probably have a card that doesn't support PCI audio, and will have to use a cable. If you do, set /dev/dspX in the capture card's configuration as the audio device. For cx88, the audiorate must be set to 48000.


=== CX88 with HD-3000 / HD-5000 ===

While the HD-3000 / HD-5500 are used to capture MPEG streams with the ATSC / QAM tuner, there is also an analog tuner on the card as well. Both HD-3000 and HD-5500 are capable of passing sound from the analog tuner over the PCI bus, saving a precious line-in jack on a sound card.

The problem is that many cards were shipped with DMA sound turned off in the prom. Luckily, a very kind fellow named ''xyzzy'' on a PCHDTV forum wrote a program to toggle this capability in the prom for HD3000 cards that don't have it turned on. The forum thread is [http://www.pchdtv.com/forum/viewtopic.php?t=1466 here.] He was kind enough to post a link to his program, [http://www.speakeasy.org/~xyzzy/download/cx88_eeprom cx88_eeprom] from within the thread. Note this program uses the module i2c-dev so it will need to be loaded before the program can read/write to the prom. Trent (program author) has kindly put some instructions in the program if it is run without any arguments. Just read and do...

One problem though, there is a kernel bug that creates a race condition when the channel is changed (or when the card is switched from Digital to Analog capture inputs). This results in no sound and some other strange picture behaviors. Again though, a kind soul, ''nybbler'' from the same forum has posted some diff's [http://www.speakeasy.net/~russotto/cx88-irq-loss-workaround.diff] and [http://www.speakeasy.net/~russotto/nodmarestart.diff]. These are a bit out of date now, so you may have to manually review the files and apply the changes in the kernel source. I did this with 2.6.20.3 and it worked perfectly for me.

So, to review:
#Build new kernel with diff's listed above
#*Download cx88_eeprom - run it for good instructions on how to proceed - summary:
#*<code>modprobe i2c-dev</code>
#*Discover which device is the cx88
#*<code>cx88_eeprom device</code> - follow instructions to toggle audio on
#Shutdown and power cycle (yes, actually turn the machine off)
#Ensure cx88-alsa is loaded - make sure new /dev/dspX device is present
#<code>mythtv-setup</code> - use new sound device /dev/dspX for sound under analog settings for DVB device
#Get a bag of chips, go to the couch, sit, watch!

Hope I didn't forget anything - feel free to edit if I have left anything out or gotten anything wrong here...

----

== EM28xx and other USB adapters ==

For most USB adapters, the '''''snd-usb-audio''''' can be loaded and used in the same way as the previously mentioned cards.


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== Driver Configuration ==

For all the supported cards, it's advisable to take care so that the capture card doesn't become the primary sound card in the system (i.e., card 0). If it does, most applications (including MythTV) will try to use it as a playout card, and it won't work. Adding this to ''/etc/modprobe.conf'' is enough to solve this:

<pre>
alias snd-card-1 ''modulename''
options snd-card-1 index=1
</pre>

For example, for '''''cx88-alsa'''''

<pre>
alias snd-card-1 cx88-alsa
options snd-card-1 index=1
</pre>


To automate the loading of the modules, you can also use ''/etc/modprobe.conf''. For example, for saa7134, add this line:

<pre>
install saa7134 /sbin/modprobe --first-time --ignore-install saa7134 && /sbin/modprobe saa7134-alsa
</pre>

== MythTV Configuration ==
Mythtv only supports OSS audio capture, which will be handled by the alsa-oss compatibility layer.  Soundcard devices will appear as /dev/dsp0, /dev/dsp1 etc. based on the card index specified.
So, for each capture card you would need to specify one of these devices for audio capture.

For example, if index=1 then you would specify /dev/dsp1 as the capture device.