ffmpeg: pass decoded or filtered AVFrame to output stream initialization

ffmpeg: pass decoded or filtered AVFrame to output stream initialization

Additionally, reap the first rewards by being able to set the
color related encoding values based on the passed AVFrame.

The only tests that seem to have changed their results with this
change seem to be the MXF tests. There, the muxer writes the
limited/full range flag to the output container if the encoder
is not set to "unspecified".