Using Xtensa side stuff or hacking mzrm communication to disable the OSD completely might be possible
There is another method:
a full-screen blank (Canon) dialog does appear to cover all Canon overlay that's on the screen during recording.
The method would work like this:
When a movie recording starts we launch a full-screen Canon dialog and immediately erase the whole screen to make the overlay disappear.
The presence of the dialog does not disable the movie button, so the recording can be stopped the usual way. When recording stops, we remove the full-screen dialog which makes the Canon overlay reappear.
Caveats:
- only tried this on my M10
- this won't disable the LOW BAT warning, so either a well charged battery or external power supply is needed
edit:
Turns out, this "great" idea doesn't work while recording - the black dialog is being redrawn constantly. That leaves the Xtensa hack as the only known way...
edit2:
Done, although not official (yet):
https://chdk.setepontos.com/index.php?topic=13489.0
