BT8x8 Active Picture Calculator

Intro:
Most analog capture cards capture part of the picture and scale it to what you asked for. The exact values depend upon the driver and the size for which you ask. The cards/driver also don't capture the center of the picture. For example, asking the BTwincap driver for 720x480 gets you 712x480 off center of a 720 line (to the left by 2 pixels), streatched to 720x480.

This calculator attempts to calculate this information based upon register readings of the BT8x8 chip. In other words, you need a BT8x8 chip to use this tool. CX288x/SAA713x/ATI chips also do this chop and streatch thing. I just don't know of a tool to read their registers. You can follow a testing procedure with a test pattern to see, but it would take some time to do for all possible driver combinations.

Currently, I only deal with horizontal streatch and center. Vertical has the same center issue, but I did not add that.


Install:
  1. You need to download BTtool.exe and bInstall.exe
  2. Run bInstall to Install the driver to talk to the chip. This requires a reboot.
Usage:
  1. Run your capture app vdub/amcap/virtualvcr/iuvcr/etc.
  2. set your desired capture size
  3. Run BTtool
  4. Type the register values in hex into the text boxes on this calculator and pick your TV standard
  5. click the calc button
  6. Crop/pad/resize based upon the info and your destination specs.
NTSC:
PAL:
Crop:
HDelay Lo:
HActive Lo:
HScale Hi:
HScale Lo:


** This was kinda tested. I can't test PAL.