Selur's Little Message Board
[BUG] Unexpected behaviour x264 and max qp - Printable Version

+- Selur's Little Message Board (
+-- Forum: Hybrid - Support (
+--- Forum: Problems & Questions (
+--- Thread: [BUG] Unexpected behaviour x264 and max qp (/Thread-BUG-Unexpected-behaviour-x264-and-max-qp)

Unexpected behaviour x264 and max qp - Brutoloco - 21.02.2021

Windows x64

The issue about max qp is not easy to explain.

Once the program starts in his default configuration and default encoder configuration. The max QP is 51 for default. (Quantization tab) And can't change this number to higher number.
I don't know if this is correct or not. But.

If I choose any AVC profile different from "High"(default profile). ---> Now max QP is 69.

If I choose back level to High, or the default config(which is also level=High). ----> QP max still in default max of 69

At this point, the only way I can the encoder behaves like at the beggining, is closing the program and starting it again.

I'm pretty ignorant about what the encoder or the program is supposed to allow or not allow. But it seems that QP MAX should be 69 by default in level High, from the beginning, without having to change from one mode to another.

I have read online that the qp from 52 to 69 is virtual. I don't know what that means. Or if I should care. I just see that there is unexpected behavior from the program.


RE: Unexpected behaviour x264 and max qp - Selur - 21.02.2021

You are correct.
Max quant should be initialized with a maximum of 69.
Since it's calculated this way: QP_MAX = 6*(CALULCATION_BIT_DEPTH-8) +15 + 18;
So for 8 bit it's 69. Not that the maximum value used for qp and crf is still 51. (since the +18 are 'virtual')
-> the initial values Hybrid uses as default will still be 1-51, but the initial maximum for the quantizer change should be 69.

Cu Selur

RE: Unexpected behaviour x264 and max qp - Selur - 21.02.2021

Send you a link to my current dev version which fixes the issue.

Cu Selur