How do you convert NTSC signal into a computer signal?

Answer 1

The best way to convert an NTSC signal into a computer signal is with a TV Frame Grabber. Buy the board, install it, and it should be able to convert NTSC video into MPEG or some other video. You will even be able to do this from RF, off the air or off of cable - just understand that some countries are digital, instead of analog - but this answer is NTSC, which is analog.

If you want to build the board yourself, consult the specifics of NTSC with Google, wikipedia, or something - it is a complex task. In high level generalities, the process is...

Build a sync separator that can differentiate between horizontal and vertical sync, and maintain the black and white reference levels.

Build an interlace detector that can detect and process the equalization pulses that occur during vertical sync. These equalization pulses are used to identify the interlacing between 29.97 Hz frame rate and the 59.94 Hz field rate.

Build a 3.58 MHz chroma oscillator that is phase locked to the chroma burst on the back porch of the horizontal sync.

Scan the data portion of each horizontal line - you will need a hardware array for each bit cell...

The luminance (black and white) data is the mean voltage between black and white reference levels at each bit cell.

The color saturation data is the amplitude of the 3.58 Mhz subcarrier at each bit cell.

The color hue data is the phase angle of the 3.58 MHz subcarrier at each bit cell.

You will need to convert the stream of bit cell data into video pixels, and then convert that into whatever PC compatible format you want.

Other things, such as closed captioning can be added by decoding the bit stream on various lines reserved for that during vertical sync.

Again, buy the board - its easier - unless you want to make a semester project out of this.