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View Full Version : x265: When to set --aq-mode 2 ?

Forteen88
30th August 2018, 19:26
Can someone please tell me in what situations I should set --aq-mode 2 in x265?
--aq-mode <integer> // Mode for Adaptive Quantization - 0:none 1:uniform AQ 2:auto variance 3:auto variance with bias to dark scenes. Default 1
--aq-mode <0|1|2|3>

Adaptive Quantization operating mode. Raise or lower per-block quantization based on complexity analysis of the source image. The more complex the block, the more quantization is used. This offsets the tendency of the encoder to spend too many bits on complex areas and not enough in flat areas.

0. disabled
1. AQ enabled (default)
2. AQ enabled with auto-variance
3. AQ enabled with auto-variance and bias to dark scenes. This is recommended for 8-bit encodes or low-bitrate 10-bit encodes, to prevent color banding/blocking.Thanks in advance.
benwaggoner
31st August 2018, 16:24
Can someone please tell me in what situations I should set --aq-mode 2 in x265?

Thanks in advance.
For distribution bitrates, I generally prefer --aq-mode 3 for SDR content and --aq-mode 2 for HDR content.

Some prefer --aq-mode 1 when absolute bang for the bit is less essential.
Gser
1st September 2018, 21:10
The only thing I've seen the other aq modes do is increase bitrate in crf mode so therefore I only use 1
benwaggoner
4th September 2018, 04:26
The only thing I've seen the other aq modes do is increase bitrate in crf mode so therefore I only use 1
Bitrate @ CRF isn't the goal; the goal is quality @ bitrate.

For SDR content, --crf 20 --aq-mode 3 may look better at the same bitrate as --crf 18 --aq-mode 1
Gser
4th September 2018, 11:56
Bitrate @ CRF isn't the goal; the goal is quality @ bitrate.

For SDR content, --crf 20 --aq-mode 3 may look better at the same bitrate as --crf 18 --aq-mode 1

My point is that I did not see any difference in quality at the same crf setting but got a bigger file size.
Forteen88
4th September 2018, 19:53
My point is that I did not see any difference in quality at the same crf setting but got a bigger file size.Did both have the similar "Avg QP" (Average QP)?
Although I'd guess (without PSY-RDO) SSIM is a better image-quality metric than Average QP.