點樣先可以cap到電視做圖?

buy a usb video capture box built-in with an AV in;
connect the AV out of your TV or video recorder to the AV in of that usb device;
then connect that capture box to your computer via usb;
usually a recording software (with frame capture) is shipped with that usb capture device;
use that software to record TV programs or capture TV screenshots.

product: Plextor capture box with TV tuner (built-in with hardware compression chip especially designed for slow machines)
around $8xx now on sale