lavu/opt: add AV_OPT_VIDEO_RATE option

Signed-off-by: Paul B Mahol <onemda@gmail.com>
lavfi/showwaves: make use of AV_OPT_TYPE_VIDEO_RATE

Signed-off-by: Paul B Mahol <onemda@gmail.com>
avutil: fix compilation

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avutil/atomic: use av_assert0()

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