All older builds are available at Index of /s905/old_builds
But I highly doubt you will get different results than with the most recent builds.
Another thing is that decoder microcode is closed source blob with no way to modify only a part of it. Porting whole microcode would most probably break decoding.
Email to [email protected] is sent:
Amlogic HEVC decoding: image quality flawed, double contours
Dear Madam or Sir,
Would you be so kind as to forward this request to your development department?Popular Amlogic S905(X) and S912 SoC devices have an unfortunate flaw:
The image quality of HEVC (H.265 / x265) video is impaired.
With hardware decoding enabled, HEVC videos show stained double contours.
This is not the case when HEVC is software-decoded.
AVC playback is not affected, comparing both shows the issue with HEVC.
Another side effect is that the bottom edge (a few pixel lines) of videos is distorted.
Both Android Marshmallow and Nougat Kernels are affected.
This is also being discussed here:[BUG] S905X (maybe all AMLogic?) HEVC decoding is flawed: bad image quality
It is a LibreELEC discussion, but Android is also affected of course.
Sample videos are attached to test and see the difference.
The community would really appreciate you getting in contact and solving this issue.Hardware HEVC decoding is one of the main selling points of these SoC, it should work properly.
Thank you in advance.
Kind regards
Let's hope it helps. 
If it does, we should also try to address the vertical lines in 2160p playback...
