In opposite to the 'xine_get_current_frame' based snapshot function this grabbing
feature allow continuous grabbing of last or next displayed video frame.
Grabbed video frames are returned in simple three byte RGB format.
Depending on the capabilities of the used video output driver video image data is
taken as close as possible at the end of the video processing chain. Thus a returned
video image could contain the blended OSD data, is deinterlaced, cropped and scaled
and video properties like hue, sat could be applied.
With this patch such a decent grabbing feature is implemented for vdpau video out driver.
If a video output driver does not have a decent grabbing implementation then there
is a generic fallback feature that grabs the video frame as they are taken from the video
display queue (like the xine_get_current_frame' function).
In this case color correct conversation to a RGB image incorporating source cropping and
scaling to the requested grab size is also supported.
A more detailed description can be found in file "xine.h".