In  issue 820313 , we check the flush function in VEA unittest. But currently the encoder of Apollo Lake platform doesn't support flush correctly. We should implement the flush and remove the boards from the blacklist of flush at:

chromiumos/src/third_party/autotest/files/client/site_tests/video_VideoEncodeAccelerator/video_VideoEncodeAccelerator.py "has_broken_flush" method.