Add -movflags rtphint documentation.
doc: add noise shaping dithers

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
swr: split swri_dither_init() out

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
swr: fix the noise sample type for noise shaping

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