h264: document h264_set_parameter_from_sps() re-calling behavior

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
mpegvideo: Increase MAX_MV for HD video

Fixes out of array reads

Found-by: Thierry Foucu
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
motion_est: Limit motion vector search range to MAX_MV

Fixes out of array reads with videos exceeding MAX_MV

Found-by: Thierry Foucu
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>