Need explanation on q and b parameter for "zones".

Navetek · 20th July 2020, 11:43

Here is the scenario: I've never before used "zones" to do any encoding, but today came across a source which I found necessary to be implemented with "zones".

So I read the documentation, and am confused with the b and q parameters. The original explanation reads:

"b=<float> applies a bitrate multiplier on the zone. Useful for extra tweaking of high- and low-action scenes.
q=<int> applies a constant quantizer on the zone. Useful for applying to a range of frames."

My questions are:

For q:
1. Does this mean that the encoder runs "Constant Quantizer" encoding mode with the q value you specified on this certain part of clip?
2. If so, why "constant quantizer" anyway, since I don't think people would use this mode ?
3. I could not find "crf" parameter available in the zones settingshttp://www.chaneru.com/Roku/HLS/X264_Settings.htm#zones, but I believe people used to set crf in zones. Why remove it?

For b:
4. Can anyone explain in detail how the "b" parameter actually works, since it is a little vague in the documentation. To be exact, how does it work in "automated 2 pass" and "constant quality" mode if there is a difference in the mechanism?

Many thanks!

20th July 2020, 11:43	#1 \| Link
Navetek Registered User Join Date: Feb 2020 Posts: 3	Need explanation on q and b parameter for "zones". Here is the scenario: I've never before used "zones" to do any encoding, but today came across a source which I found necessary to be implemented with "zones". So I read the documentation, and am confused with the b and q parameters. The original explanation reads: "b=<float> applies a bitrate multiplier on the zone. Useful for extra tweaking of high- and low-action scenes. q=<int> applies a constant quantizer on the zone. Useful for applying to a range of frames." My questions are: For q: 1. Does this mean that the encoder runs "Constant Quantizer" encoding mode with the q value you specified on this certain part of clip? 2. If so, why "constant quantizer" anyway, since I don't think people would use this mode ? 3. I could not find "crf" parameter available in the zones settingshttp://www.chaneru.com/Roku/HLS/X264_Settings.htm#zones, but I believe people used to set crf in zones. Why remove it? For b: 4. Can anyone explain in detail how the "b" parameter actually works, since it is a little vague in the documentation. To be exact, how does it work in "automated 2 pass" and "constant quality" mode if there is a difference in the mechanism? Many thanks!