avisynth: Introduce USING_AVISYNTH macro

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avisynth: Change most of the comments to /* */ from //

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

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avisynth: Compact AvxSynth's avoidance of 2.6's colorspaces.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avisynth: Don't declare structs anonymously

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avisynth: Remove a couple of useless AviSynthContext casts

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avisynth: Remove outdated undef block

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avisynth: Use AV_* prefixes for video and audio IDs

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avisynth: Switch a couple of AVERROR_UNKNOWNs to AVERROR(ENOMEM)

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avisynth: Simplify a stray av_log message

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avisynth: Factor out a couple of returns

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