AFAIK:

The TV-out connectors in the dvb-ttpci board output automatically NTSC
if the stream is NTSC. They output automatically PAL when the stream is PAL.

When there is no stream (channel switch or the like), they output PAL by
default, or NTSC if the tv_standard kernel option is used to select that.

The output from /dev/video0 file is PAL all the time, unless it is
changed by the proper V4L ioctl, which is done by VLC and v4lctl.

This is exactly what I have observed as well. Is there any way VDR could perform this V4L ioctl without the need for external applications such as VLC and v4lctl?

Best Regards.