There are 4/5 tv encoder manufacturers:
- Philips with their SAAxxxx chipsets
- Brooktree with their BT 8xx chipsets
- Chrontel with their chipsets
- Conexant (these chips are Brooktree compatible)
- Nvidia with their builtin TVout encoders on most GF4 MX boards
One thing you need to do first is to use optimal tvout resolutions. For NTSC the max resolution is 640x480 @ 60Hz and for PAL 800x600 @ 50Hz. Don't choose a resolution higher than these since higher are scaled back ...
Also make sure that you use an S-video connector to connect the videocard to the TV. Composite really sucks.
Something else you can use for tvout is a tool called nvtv located at http://www.sourceforge.net/projects/nv-tv-out.
This tool uses its own tvout implementation (not working with the stuff from the drivers) but it can do a lot more. Custom tvout resolutions, flickering tweaking ......