Question / Help Max Bitrate

[SuperN00b]

I've been using Elgato's HD60 for capture for years with no issues (also briefly had a Cam Link 4K before selling it). However, for some reason recently, Elgato's Game Capture (and 4K Capture Utility in the Cam Link's case) decided it didn't like my HP Zbook or my new MacBook Pro or iMac (both high-spec'd, new machines). I gave up on Elgato tech support-very responsive, but things were getting lost in translation. So I started using OBS for capture, and with the right settings, it works flawlessly on both platforms.
I also just upgraded to the HD60 S+ for the higher bitrate (60 Mbps vs 40). My question is this: In the Advanced mode, OBS allows you to set your own capture bitrate. Am I gaining anything by setting the bitrate to higher than 60 (e.g. 80 or 100) in OBS? Or does the device kneecap it at 60 anyway?
(Related, does anyone happen to know the bitrate ceiling for the upcoming [still vaporware] Elgato 4K60S+?)

 

[R1CH]

The capture device should send an uncompressed signal to OBS, the bitrate listed in the specs only matters when you use the Elgato recording software. For recording, you should be using CRF / CQP though and not a fixed bitrate. This lets the encoder use as much bitrate as it needs to hit the target quality.

 

[SuperN00b]

The capture device should send an uncompressed signal to OBS, the bitrate listed in the specs only matters when you use the Elgato recording software. For recording, you should be using CFR / CQP though and not a fixed bitrate. This lets the encoder use as much bitrate as it needs to hit the target quality.

Thanks very much R1CH! I am not familiar with CFR. Are there recommended settings for optimal results, e.g. CRF, Keyframe Interval (presumably 30 for 60 fps capture?), CPU Usage Preset, Profile, etc? (I am capturing on a 2018 MacBook Pro, Core i9, 2.9 GHz.)
TIA!

 

[Harold]

CRF, not CFR, he typo'd.
CRF and CQP are quality based rate controls.

 

[R1CH]

The best way is just to experiment, make some recordings at different settings and see how they look. There are no general settings that fit all use cases. A CRF value of 15 is generally high quality, lower numbers are higher but will increase bitrate.

 

[SuperN00b]

The best way is just to experiment, make some recordings at different settings and see how they look. There are no general settings that fit all use cases. A CRF value of 15 is generally high quality, lower numbers are higher but will increase bitrate.

I am confused. A lower CRF value increases the bitrate? I just need a recommendation on what I should change it to. Currently the default value for CRF is 23 (on my machine). So is that too high? Too low? (Last question before I give it a go, I promise!)
Btw, based on your answer(s) here, my guess is that the same practices will apply to the 4k60S+ as well. ("It's the software, stupid!" :))

 

[carlmmii]

Try a CRF value and see how the output looks. If you need higher quality, lower the CRF value (think of it as how far from "exact" the output is).

The same principle applies to any capture card, as long as the capture card is sending and uncompressed signal to the computer. I'm not certain if the 4k60S+ actually is uncompressed though -- there isn't enough bandwidth over usb3.0 to send a full 4k60 feed, so it is definitely having to send a compressed signal for that... but I don't know if it has the ability to send an uncompressed feed for lower resolutions.

Regardless though, if the quality of the image coming from the capture card is higher than what you're eventually compressing to, then all that usually matters is your own compression settings.

 

[SuperN00b]

Thanks for all the replies here, folks. I have CRF set to 6 and have been getting really nice quality captures a ~70-80 Mbps. It's a shame Elgato's software is so flaky.

 

[Harold]

Below about CRF 14, diminishing returns start kicking in HARD. You generally don't need any lower than 14 to get near-lossless picture quality.

 

[SuperN00b]

Below about CRF 14, diminishing returns start kicking in HARD. You generally don't need any lower than 14 to get near-lossless picture quality.

Thanks, Harold. I will continue to experiment. At 15, I was getting somewhere around 40-50 Mbps. Not a huge deal. But my plan is to be able to edit/color edit. SO maybe I am mistaken to think a higher bitrate is better than for editing?

 

[Harold]

Indeed. Using CRF as your rate control gives the encoder a quality target to match and allows the encoder to decide for itself what bitrate to use.
Near-static content will automatically use a lower bitrate and high motion content will automatically use a higher.