Doing some research shows that the timings for the S-video TV output is hardcoded in the Radeon driver to a set number of TV standards e.g. PAL, NTSC, etc
The code for the timings and TV standards for the S video TV output can be found in the radeon_legacy_tv.c file
https://code.woboq.org/linux/linux/d...gacy_tv.c.html
Thanks
Thierry