On Sat, 2010-06-12 at 16:20 -0400, Dale Pontius wrote:
> On 06/12/10 08:42, Andy Walls wrote:
> >> It's just flakey. Maybe when I get a break and take this system down, a
> >> bit of dust-off and reseating cards will work wonders.
> >
> > Well, some things to try:
> >
> > 1. remove all instances of the cx18-alsa.ko module from
> > under /lib/modules. It shouldn't matter, but most users never need it,
> > If hald or pulseaudio has it open, you may be unable to switch away from
> > 48 ksps and then back.
>
> My kernel is getting a little long in the tooth, so it wouldn't hurt me
> at some point to build a new one. 2.6.33 seemed a bit disruptive to
> lirc, but I think that's worked around by now.
>
> Do I even need cx18-alsa?
If your only use case in MPEG TV capture/recording, then No.
If you have other use cases for capturing non-MPEG compressed audio and
video and don't mind complex and arcane command lines, then the answer
is also No.
> I sort of built it because it was there and I
> have a cx18, even though I never needed it before. What is cx18-alsa
> for, anyway?
It presents an ALSA "sound card" interface, with a control device node
and PCM capture device node, to user space for the PCM audio stream
available from the CX23418 encoder (the digital audio before the MPEG
encoder applies MPEG compression to it).
The V4L2 API provides an interface to userspace for PCM audio capture
from /dev/videoN nodes such as /dev/video24. However the
common/popular/GUI apps on linux that process or play audio normally
expect and ALSA or OSS interface, and don't know how to manipulate V4L2
controls nor look for /dev/video* device nodes for PCM audio.
The only real reason to use cx18-alsa is so that GNURadio (GNOMERadio ?)
works with an CX23418 board with FM radio. GNURadio knows to
open /dev/radio for control and expects audio to come from an ALSA PCM
device node - not /dev/video24.
Once tvtime is all fixed up, one could easily use a CX23418 board as a
dumb framegrabber, using /dev/video32 for uncompressed YUV video frames
and the ALSA device nodes for sound. That saves of the overhead of MPEG
decompression for watching Live TV. It also would be easier to play
video games through the CX23418 based card using tvtime.
Right now, if you want to hear the uncompressed audio hitting the
CX23418 encoding engine, just use
aplay -f dat < /dev/video24
while tuned to a channel (an MPEG or YUV capture need not be in
progress) and set to 48 ksps (for the -f dat parameter)
If you want to listen to FM radio on a card that supports it:
ivtv-radio -d /dev/radio0 -i /dev/video24 -f 101.5
which you will notice spawns aplay to play the audio.
Regards,
Andy
> Dale
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