Kworld ATSC 120 audio capture bug

Kworld ATSC 120 audio capture bug

[Vanessa Ezekowitz]

While setting up to rip an old movie from a video tape (one which is not available on any other media), I ran into a bug in the cx88 driver..

As in the past, I can initialize the card into analog mode after a reboot, and view video feeds from over-the-air analog TV (what little remains anyway), composite video in, and svideo in just fine.  Audio for the TV also works fine via the cx88-alsa driver, as usual.

However, for some reason, switching to either composite or svideo input does *not* switch the audio input to the two RCA jacks on the harness like it should.  Instead, when I switch to composite mode I get the TV audio from the last channel I tuned to, plus a little crackling or static (probably feedback from the VCR I have connected to that input), and plain white noise when I switch to Svideo mode.

Just to be sure it wasn't an outdated driver, I cleaned up my kernel configuration, fetched a fresh copy of the v4l-dvb repository, and built/installed it, then rebooted and tried again.

Using `xawtv -noxv` for video and sox for the audio stream, as usual for these kinds of tests.

I could swear that this used to work some time back, but I can't make even a rough guess as to when it quit working.

-- 
"There are some things in life worth obsessing over.  Most
things aren't, and when you learn that, life improves."
http://starbase.globalpc.net/~vanessa/
Vanessa Ezekowitz <vanessaezekowitz@gmail.com>

Re: Kworld ATSC 120 audio capture bug

[Trent Piepho]

On Sat, 28 Mar 2009, Vanessa Ezekowitz wrote:
> While setting up to rip an old movie from a video tape (one which is not available on any other media), I ran into a bug in the cx88 driver..
>
> As in the past, I can initialize the card into analog mode after a reboot, and view video feeds from over-the-air analog TV (what little remains anyway), composite video in, and svideo in just fine.  Audio for the TV also works fine via the cx88-alsa driver, as usual.
>
> However, for some reason, switching to either composite or svideo input does *not* switch the audio input to the two RCA jacks on the harness like it should.  Instead, when I switch to composite mode I get the TV audio from the last channel I tuned to, plus a little crackling or static (probably feedback from the VCR I have connected to that input), and plain white noise when I switch to Svideo mode.

Because of the way the ADC on cx88 chip works it can't record sound from a
audio line in.  It can only record sound that comes from a tv tuner.
Typically the audio line in on a cx88 card is only a pass-through to the
line out connector on the card.  There is usually a mux that switches the
line out from TV audio to the line.  You'd connect the line out from the
cx88 card to your sound card's line in and listen/record with the sound
card.

Now, it is possible for a cx88 card to have an external ADC chip, in which
case that ADC can be used to record line level audio.  Only a few (one?)
cx88 cards have this and I don't know if yours does.  So maybe this broke
for your card, but I think it's more likely what you're remembering is
recording with your sound card.