Bug Report Abnormal CPU usage at 60 fps

vopeju

New Member
I was messing around with some settings since my (completely separate from OBS) local recording setup was giving me some new issues with framedrops ingame. While doing that, I noticed OBS studio's CPU usage was much higher than I remember it being the last time I had to screw around with all this, which was back when I used OBS classic. I was expecting usage of around 20%, and was getting 30%+.

further experimentation led to these numbers showing up on the self-reported CPU meter.

at 30 fps: 6-7% on average
at 48 fps: 10-12% on average
at 59.94 fps: anywhere from 10-20%
at 60 fps: 30-40%, averaging 35%

cpu usage as reported in taskmanager was typically a bit higher while streaming (but I didn't check that much). thankfully, my immediate workaround has already presented itself. . . 59.94 here i come

log https://gist.github.com/a9f2ac5914da909afad10c2c17e6e2e5

[edit] some more testing.

at 59.94 fps, if I disable all sources besides the game capture, don't stream & just look at the preview, obs uses 2-4% cpu. reentering the game (usually) causes a spike to 20-25% usage, and then a few seconds later, it begins slowly dropping back down to 3-4%, barring semi-frequent spikes to 10%+.

on the other hand, if I swap from 59.94 to 60 while alt-tabbed, nothing happens. When I reenter the game, it jumps up to 25% and stays pegged there, even if I alt-tab again. Swapping back to 59.94 causes it to drop again.

25% seems a fairly significant number to me, considering that I have a 4 core cpu.
 
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first of all set windows to high perf mode in power management - it will keep cpu at max clock all the time, without it when you alt tab cpu load drops, clocks are slowed down and obs shows different usage. x264 also changes cpu usage when it doesnt analyze image because game is alt tabbed
to measure cpu load run HWInfo in sensor mode in background while streaming/recording without alt tabbing and check max cpu usage after stopping, then second time game only without obs and compare. alt tabbing causes processes to go semi-sleep mode and breaks the results
also running obs at 59 and playing at 60 desynchronizes source (game) with output stream/recording and will most probably cause video stutters - it doesnt apply if you run obs at half rate of gaming refresh rate
 
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