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-
-Intro
-=====
-
-people start bugging me about this with questions, looks like I
-should write up some documentation for this beast. That way I
-don't have to answer that much mails I hope. Yes, I'm lazy...
-
-
-You might have noticed that the bt878 grabber cards have actually
-_two_ PCI functions:
-
-$ lspci
-[ ... ]
-00:0a.0 Multimedia video controller: Brooktree Corporation Bt878 (rev 02)
-00:0a.1 Multimedia controller: Brooktree Corporation Bt878 (rev 02)
-[ ... ]
-
-The first does video, it is backward compatible to the bt848. The second
-does audio. btaudio is a driver for the second function. It's a sound
-driver which can be used for recording sound (and _only_ recording, no
-playback). As most TV cards come with a short cable which can be plugged
-into your sound card's line-in you probably don't need this driver if all
-you want to do is just watching TV...
-
-
-Driver Status
-=============
-
-Still somewhat experimental. The driver should work stable, i.e. it
-should'nt crash your box. It might not work as expected, have bugs,
-not being fully OSS API compilant, ...
-
-Latest versions are available from http://bytesex.org/bttv/, the
-driver is in the bttv tarball. Kernel patches might be available too,
-have a look at http://bytesex.org/bttv/listing.html.
-
-The chip knows two different modes. btaudio registers two dsp
-devices, one for each mode. They can not be used at the same time.
-
-
-Digital audio mode
-==================
-
-The chip gives you 16 bit stereo sound. The sample rate depends on
-the external source which feeds the bt878 with digital sound via I2S
-interface. There is a insmod option (rate) to tell the driver which
-sample rate the hardware uses (32000 is the default).
-
-One possible source for digital sound is the msp34xx audio processor
-chip which provides digital sound via I2S with 32 kHz sample rate. My
-Hauppauge board works this way.
-
-The Osprey-200 reportly gives you digital sound with 44100 Hz sample
-rate. It is also possible that you get no sound at all.
-
-
-analog mode (A/D)
-=================
-
-You can tell the driver to use this mode with the insmod option "analog=1".
-The chip has three analog inputs. Consequently you'll get a mixer device
-to control these.
-
-The analog mode supports mono only. Both 8 + 16 bit. Both are _signed_
-int, which is uncommon for the 8 bit case. Sample rate range is 119 kHz
-to 448 kHz. Yes, the number of digits is correct. The driver supports
-downsampling by powers of two, so you can ask for more usual sample rates
-like 44 kHz too.
-
-With my Hauppauge I get noisy sound on the second input (mapped to line2
-by the mixer device). Others get a useable signal on line1.
-
-
-some examples
-=============
-
-* read audio data from btaudio (dsp2), send to es1730 (dsp,dsp1):
- $ sox -w -r 32000 -t ossdsp /dev/dsp2 -t ossdsp /dev/dsp
-
-* read audio data from btaudio, send to esound daemon (which might be
- running on another host):
- $ sox -c 2 -w -r 32000 -t ossdsp /dev/dsp2 -t sw - | esdcat -r 32000
- $ sox -c 1 -w -r 32000 -t ossdsp /dev/dsp2 -t sw - | esdcat -m -r 32000
-
-
-Have fun,
-
- Gerd
-
---
-Gerd Knorr <kraxel@bytesex.org>