Frequently Asked Questions
--------------------------

Q: Are you related to Ewald Snel?
A: Not that I know of.

Q: The image keeps moving and the colors are wrong.
A: The program tries to lock on to the start of a white line with
   a length between 335 and 365 pixels, preceded by a black line
   of at least 50 pixels. Most television channels have such a line.
   (white means: level > 50 and black means LEVEL <= 50).

   The sync/lock code is not perfect, you may need to switch channels
   a couple of times for it to find the line. It works quite well
   for me.

Q: The image gets inverted all the time.
A: cc2y4m looks at a pixel just after the end of the active picture,
   if it is white it inverts the output, otherwise not. In the future
   there may be command line options to change the behaviour of the
   program. For now: edit the source.

Q: I get junk on the screen when I run your program.
A: You should pipe the output of the program to mplayer(1), see
   the README.

Q: What does cc2y4m stand for?
A: Well, it's a conversion program. So the '2' stands for 'to', as in
   ps2pdf(1). 'y4m' means YUV4MPEG2. 'cc' stands for 'PAL which laCks synC,
   and maybe other unwanted junk'.

Q: I get no sound. Why?
A: Some channels encode the sound at the right side of the active
   picture (where the vertical sync used to be). It is encrypted,
   the encryption alogrithm is unknown.

Q: The image flashes a little at a frequency of 10Hz, can it be fixed?
A: Probably, send a patch.

Q: After a black region in the image, brighter parts become too bright. Why?
A: Well, if I understand the datasheet of the BTTV chips correctly,
   the ADC reference voltage is supplied throug an 'Automatic Gain 
   Control' circuit (AGC). It adjusts the reference voltage of the ADC to 
   what it thinks to be an appropriate value.
   
   If the horizontal sync region is not black enough the AGC will get 
   confused, and the ADC will become oversensitive to grey signals after a 
   period of black.  It is possible to turn the AGC off but ONLY if an 
   external reference voltage is connected to the chip, which is not the 
   case in my red PCTV Rave.

Q: Can it be fixed?
A: It may be possible to do it in software. If the AGC-theory is 
   correct, a hardware solution may also be possible. As in: connect
   the reference voltage pin of the Bt87[89](A) to a suitable reference
   voltage and instruct the card (in software) to turn off AGC.

Q: Does it also work on non Bt87[89](A) chips?
A: Currently not. But it is probably easy to make it work on the Bt84[89](A).
   The reason is that the Bt87[89](A) allows the vertical scrolling to be
   controlled with the vertical total register, which is easier to use
   that the PLL, I'm just lazy. (and I don't have a Bt84[89](A))

Q: Will it in the future work with chip XXXX?
A: Well, it depends on the properties of that chip. It needs to be
   able to ignore sync signals; it needs to have an adjustable PLL 
   and it needs to have a raw capture mode. If all these conditions
   are satisfied it may be possible to support that chip with this program.

Q: Will the be a Windows 95/98/ME/NT/2000/XP/whatever version of this program?
A: Not from me, but maybe someone will port it.

Q: How does the locking routine work?
A: See the file TECH for an answer.

$Id: FAQ 38 2004-06-24 19:00:24Z rsnel $
