doc/utils: rewrite doc for time duration syntax

Extend description and clarify syntax.

Signed-off-by: Timothy Gu <timothygu99@gmail.com>
Signed-off-by: Stefano Sabatini <stefasab@gmail.com>
doc/utils: reformat doc for color syntax and add list of supported colors

Signed-off-by: Timothy Gu <timothygu99@gmail.com>
Signed-off-by: Stefano Sabatini <stefasab@gmail.com>
doc/filters: reference ffmpeg-utils manual for color and sizes options

Signed-off-by: Timothy Gu <timothygu99@gmail.com>
Signed-off-by: Stefano Sabatini <stefasab@gmail.com>
swscale/swscale_unscaled: fix alpha pointer & stride for planarRgb16ToRgb16Wrapper()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
swsscale/swscale_unscaled: add GBRAP16

Signed-off-by: Paul B Mahol <onemda@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>