Comment by retrac

The new RP 2350 has an enhanced PIO that relaxes some of the constraints the author ran into here.

Also the new HSTX (high-speed serial transmit) unit is really well suited for rapid line coding.

Here's a different project that generates a high resolution high depth VGA signal from the RP 2350: https://www.breatharian.eu/hw/disphstx/index_en.html

And here's NTSC composite using just the original PIO: https://github.com/obstruse/pico-composite8