HEVC HW encoding quality/bitrate issue on SKL

[Jianlin_Q_Intel]

Hi,

We're testing MediaSDK HEVC HW encoding on SKL (with Iris Pro 580). Media SDK version 1.13.

We found the bitrate/quality is not satisfactory when the test scenario is Video conferencing, which normally have static background, and foreground with low motion. 

We use the lastest MSDK sample_encode against MSDK 6.0.0.388. The input image is 300-frame I420 of 720p captured from camera. Two groups of test is conducted:

1.  Compare bitrate/PSNR of encoded HEVC with AVC, using the same QP value 26 at CPQ mode.  The encoded image contains only I/P frame. GOP size is open. NumRef =1.  Target_Usage=balanced, framerate=30.

2.  Compare bitrate/PSNR of encoded HEVC with AVC, using the same bitrate 1500kbps at CBR mode. The encoded image contains only I/P frame. GOP size is open. NumRef=1, Target_Usage=balanced, framerate =30.

Here is the result:

Codec	BRC	QP	File Size	PSNR
AVC	CBR	N/A	1761 KB	43.241845
HEVC	CBR	N/A	1826 KB	42.932315
AVC	CQP	26	1845 KB	43.467997
HEVC	CQP	26	2692 KB	44.283313

Such kind of result is far from satisfactory.  We and our customer expect at CQP mode the bitrate of HEVC is 40% lower than AVC, but now it's nearly 50% higher.   We expect at CBR mode the video quality of HEVC to be better but however it has lower PSNR.

Have you tested the video conferencing scenario, or are you aware of any specific settings we could apply to get better PSNR for HEVC at CBR mode, and lower bitrate for HEVC at CQP mode?  Thanks!