Fix wmv1 decoding if no other msmpeg4-related decoder was compiled.
Fix wmv1 encoding if all other msmpeg4-related encoders were disabled.
avcodec/mpegvideo: clip mv visualization arrows so that their direction is maintained

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avformat/m4vdec: raise threshold slightly for detection

Fixes Ticket3746

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avutil/bprint:ædd io.h, try to fix msvc build

Suggested-by: jamrial
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>