[BUG] S905X (maybe all AMLogic?) HEVC decoding is flawed: bad image quality

boot2k3 · August 15, 2017 at 4:42 PM

Quote from kszaq

3.14.29 in no way identifies kernel git revision, it is a base for all S9xx Amlogic kernels.

Could you give me a command to identify this revision?

**afl1** · August 15, 2017 at 5:24 PM

In box KIII Pro (S912) with Android 7.1.1 this issue is presented.

**kszaq** · August 15, 2017 at 5:30 PM

Quote from boot2k3

Could you give me a command to identify this revision?

The only way I know is to ask firmware provider.

jd17 · August 15, 2017 at 6:00 PM

Quote from afl1

In box KIII Pro (S912) with Android 7.1.1 this issue is presented.

The box from boot2k3 uses Android 6 and the issue is not present, yours is on 7 and it is.

Could we not compare the code for HEVC decoding on these two to identify the difference?

boot2k3 · August 15, 2017 at 6:26 PM

I don't know if it means but I see this difference between Android and LibreElec:

Android: Video decoder: amc-h265 (HW)

pixel format: Surface

LibreElec: Video decoder: am-h265 (HW)

pixel format: unknown

**kszaq** · August 15, 2017 at 6:32 PM

Quote from jd17

Could we not compare the code for HEVC decoding on these two to identify the difference?

We don't have source code for them.

Quote from boot2k3

Android: Video decoder: amc-h265 (HW)

pixel format: Surface

LibreElec: Video decoder: am-h265 (HW)

pixel format: unknown

AMC is Android Media Codec which is a proxy layer between Android apps and AMCodec.

**kszaq** · August 15, 2017 at 7:14 PM

I checked Android 6.0 on my S912 box: issue is present.

jd17 · August 15, 2017 at 7:15 PM

Could you extract the Kernel from boot2k3's Android?

**kszaq** · August 15, 2017 at 7:36 PM

If he shares kernel image... but then what? I don't follow what you want to do with it.

jd17 · August 15, 2017 at 7:39 PM

I am desperately grasping for straws.

Could you create a LibreELEC build based on that Kernel?
That was my idea...

**kszaq** · August 15, 2017 at 7:45 PM

No, I can't. I need kernel source code to build LE image. Besides, Marshmallow kernel would be a step back.

jd17 · August 15, 2017 at 7:54 PM

OK, sorry to hear it.

I know that Marshmallow would technically be a step back, but I would prefer flawless HEVC playback over the benefits of Nougat.

Do you have any other ideas?
What about contacting AMLogic? Is that somehow possible?

**kszaq** · August 15, 2017 at 8:00 PM

All my devices (S905X, S912) running Android 6 have this issue.

Unfortunately I don't have any way to contact Amlogic.

jd17 · August 15, 2017 at 8:13 PM

Have you ever tried just getting in contact "the usual way"?
Amlogic -晶晨

Technical: [email protected]

I mean... all they can say is no.
Best case scenario - they actually refer you to a developer.

I'd offer to do it, but all I can do is link to this thread.
You however could actually get into the technical details of the code with them...

yatoya · August 16, 2017 at 12:50 AM

It's not white. It's just sharper.

All my x265 seems to sharper than x264 but the difference is really little.

I wouldn't notice it if not this thread. Nothing that bothers me.

frequenzy · August 16, 2017 at 3:03 AM

also can't notice the difference, must be my eyes.

jd17 · August 16, 2017 at 8:29 AM

A type of edge enhancement could certainly be responsible for the double contours.

Maybe another route to investigate:
wrxtasy recently told us about AMLogic's always-on Noise Reduction...

Maybe something similar applies to HEVC decoding?
Something like (pseudo):

for hevc

edge_enhancement=1

...or...

for hevc
sharpness=+2

Just an idea...?

jd17 · August 16, 2017 at 12:57 PM

Quote from kszaq

Amlogic modifies their decoder from one kernel release to another and it's quite possible that the issue was not present at some point.

I am happy to test various older generations of your builds (before 7.0.3.012) - maybe I will find an "HEVC decoding gem".
Could you make these accessible to me? The old download links are all down (7.0.3.011 and older)...