vf_overlay: add eof_action switch

Signed-off-by: Anton Khirnov <anton@khirnov.net>
utvideoenc: Add support for the new BT.709 FourCCs for YCbCr

With cli usage the decoder might have not set the colorspace during
encoder init, manual colorspace override might be needed in such
cases.

Signed-off-by: Anton Khirnov <anton@khirnov.net>