tests/filtergraphs/overlay_nv21

sws_flags=+accurate_rnd+bitexact;
split [main][over];
[over] scale=88:72, pad=96:80:4:4 [overf];
[main] format=nv21 [mainf];
[mainf][overf] overlay=240:16:format=yuv420, format=yuv420p