doc/filters: add sepia example for colorchannelmixer

Signed-off-by: Paul B Mahol <onemda@gmail.com>
avfilter: fix preprocessor condition

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avformat/matroskaenc: Only change chapter ids if needed.

This also fixes the case where negative chapter ids where input
And fixes the case where remuxing from mkv changed chapter ids

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