UHD Buffer setting?

[kpic]

So I set my .ini file in BDRB to a UHD maxrate of 37,500 using the "UHD_MAXRATE" setting, I have noticed in the films I have done this in there is still a maximum spike in several instances of going way over that 37,500 cap.

I noticed that there is another setting in the Hidden Opts: UHD_VBV_BUFFER

Does this UHD Buffer setting also need to be incorporated into the .ini file to get a more stable bit-rate?

If so and I do a maxrate of 37,500 should the buffer also be set as 37,500. Guess I'm just confused if that buffer setting also needs to be set in order to get a maximum bit-rate cap or if it's a 'nothing to do with bit-rate' setting?

[jdobbs]

Look at the command line in LASTCMD.TXT (in the rebuilder folder) and see what maximum rate is being passed to the encoder. It would have to be right after the encoding, as the last command changes for each encode process.

[kpic]

Looks fine in the Lastcmd.txt file: --vbv-maxrate 35000

This was for the most recent project where I set the maxrate to:35,000 (with no VBV Buffer setting so I guess the default is 45,000?) that had several scenes over 40000 or so those were fine but I also had a scene or two of near 49,000 (Sony, Oppo & Cyberlink).

To go from 35,000 to 49,000 is pretty bad control, that's why I was wondering if the VBV Buffer setting has something to do with the spikes in bit-rate as well?

[Emulgator]

If the VBV model wouldn't allow for spikes that the buffer would be able to hold, then it would sacrifice quality for that occasional burst of hard-to-compress-frames.
I would expect those spikes to happen, and welcome them, as long as the VBV constraints are met.

[kpic]

Forgot to update this thread... I did a version using these settings;

CUSTOM_TARGET_SIZE=39000
UHD_MAXRATE=34000
UHD_VBV_BUFFER=37000

Those settings got me a version that was very much like a constant bitrate version. There were no high spikes but it also didn't act like a variable bitrate either, the bitrate hovered around 32000 to 36000 pretty much for the entire film no matter the scene (low action - high action). So it seems to set some sort of CBR mode in UHD?

The reason I was doing it this way is I was putting this one on a BR disc so I couldn't have bitrate spikes too high as it would cause the player to freeze at that mark. Now with a more constant bitrate the player goes right through those problem scenes from before. The downside is that I'd rather it be more of a VBR so that it would go down when needed but be capped at a (not too) high setting as I was looking for in the original post. So this way it worked but still not as I'd expected.