lavfi/smptebars: fix output for subsampled yuv

Signed-off-by: Paul B Mahol <onemda@gmail.com>
lavfi/blend: add N variable

Signed-off-by: Paul B Mahol <onemda@gmail.com>
avutil/opencl: add check for the program number to create kernel

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avutil/opencl: check strtol for failure

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avutil/opencl: replace assert by check and error message in av_opencl_init()

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