separatefields filter

Signed-off-by: Paul B Mahol <onemda@gmail.com>
avformat/avisynth: Fix off-by-one error in avisynth demuxer.

Fixes ticket #2412.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avformat/avisynth: Cosmetics

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