[vdr] How To use DeviceStillPicture ?

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.