lavfi/blend: use dual input helpers

Signed-off-by: Paul B Mahol <onemda@gmail.com>
replace some deprecated defines

Signed-off-by: Paul B Mahol <onemda@gmail.com>
avformat/utils: factor ff_find_last_ts() out of ff_gen_search()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
nutdec: use ff_find_last_ts()

Fixes finding the duration for nut files that are truncated

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