[vdr] How To use DeviceStillPicture ?

[Martin Dauskardt]

I have seen that plugins use this in a different way.

For example in this order:
	DevicePlay
	DeviceStillPicture
	DeviceFreeze
So the next action to display a new Stillimage would start with DevicePlay

Others call neither Freeze nor Play. The dvd-Plugin calls DeviceClear and 
DevicePlay before DeviceStillPicture.

I remember that Klaus once stated that DeviceStillPicture could be seen as a 
trickmode, so that always a Play has to follow to resume from trickmode. But 
is it necessary to Freeze the Stillpicture before?

And I wonder: How should a device plugin handle the StillPicture function? Is 
it necessary that StillPicture also calls a Clear()  to clear the internal 
decoder buffers? It looks like that vdr is not doing this in dvbdevice.c, 
although I am not sure if  the av7110 ioctl VIDEO_STILLPICTURE does 
internally clear the buffers. 

I noticed problems when both plugins (that one that uses DeviceStillPicture 
and the device plugin) do a Clear() at the same time.