drgeoff wrote:No, for a multitude of reasons including the one that the GPIOs are logic outputs (high or low) and the chrominance signal is analogue.
redhawk wrote:The GPIO output pin can be either 3.3v or 0v it would not be possible to generate a chrominance signal.
If you want S-Video output then you'll need a HDMI video converter box with S-Video or Y/C support.
Both of these issues are easily addressable with a DAC that outputs 0.3v peak-to-peak. Or a DAC that is fed into a common-emitter Class-A "amplifier" with lower-than-unity gain.
You seem confused on several points:
1. The chrominance signal can be pretty close to 1 volt peak to peak (100% colour bars).
2. Each GPIO is a 1-bit output. You need around 8 bits of resolution for the chrominance signal. For low frequency signals (such as audio) a 1-bit output can be operated in a pulse width or pulse density mode to act as a D to A. The RPi can achieve about 11 bits resolution for 48 kHz samples. The chrominance signal needs samples at more than 7.2 MHz (NTSC) or 8.9 MHz (PAL). That would yield about 3 bits of resolution.
3. Anyway all of #2 above is irrelevant. There is no pathway within the chip which can route signals from the video output side of the GPU to the GPIO pins.