Make decoding alpha optional for some codecs.

For codecs where decoding of a whole plane can simply
be skipped, we should offer applications to not decode
alpha for better performance (ca. 30% less CPU usage
and 40% reduced memory bandwidth).
It also means applications do not need to implement support
(even if it is rather simple) for YUVA formats in order to be
able to play these files.

Signed-off-by: Reimar Döffinger <Reimar.Doeffinger@gmx.de>
avfilter: add ladspa wrapper filter

Signed-off-by: Paul B Mahol <onemda@gmail.com>
avcodec/sgirledec: fix infinite loop in decode_sgirle8()

Fixes #2985.
Reported-by: Piotr Bandurski <ami_stuff@o2.pl>
Signed-off-by: Paul B Mahol <onemda@gmail.com>
lavc: Add support for interleaved chroma formats to libx264. Interleaved chroma is x264's native format

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