...at least with the newest nightly x64 build, Avidemux v2.7.0 (170517_23bc4fdf09d).
Just noticed because I couldn't decode/view a file, noticed that Lavcodec is used instead of DXVA2, checked back with a stable 2.6.19 (I know, not the newest, but had it still on my HDD) and there my file played back well using DXVA2.
Any use for a snippet of my file (mp4, AVC+AAC, encoded by Lavf56.15.102 according to mediainfo)?
This regression is exactly the reason why the 2.6 "support" branch using older ffmpeg exists in the first place.