frames dropped due to rendering lag but GPU usage is low

[deadtomb]

I'm running a very simple scene on my slow slow macbook. The scene is basically a video play back and a camera capture placed left and right. I didn't use streaming nor recording since the scene is to be projected via HDMI. The problem is that frame dropped due to rendering lag is very high. ( it starts low but gets higher and higer, up to like 50%, and when it goes that high the audio and video gets out of sync).
I was told that rendering is done by GPU, but the problem is the GPU usage is only a little over 10% or so. History graph shows that GPU never exceeds 40%. But the CPU is running quite high. Does that mean that OBS is actually using the CPU to do the rendering work? I tried to change the codec but x264 or apple VT does not make a difference. ( I suppose the codec only affects the encoding stage, rather than the rendering stage).

 

[InSinkProductions]

I used to have a similar issue. My mac is old but fairly powerful for it's age. My experience is that my GPU is barely being used, but my CPU is getting close to it's limits when render lag starts. I have an extremely bloated scene with 4 monitors and multiple display captures, and a ton of Apps I run during the stream. The number 1 solution to help reduce CPU usage (albeit at at cost - Quality loss), is raising Your CPU preset higher - Settings>output>streaming>cpu usage preset - The higher you go, the less CPU is tasked. Start one higher than where you are now, eg. faster - change to veryfast. If that isn't good enough, up it to superfast and then ultrafast. Again, if you go too high, this will pixilate a little when being pushed a bit, but your render lag will be gone. It will still look way better than tons of dropped frames due to render lag. If none of that helps, lower your resolution. 720 instead of 1080 etc. and 30fps vs 60 fps.

 

[deadtomb]

I used to have a similar issue. My mac is old but fairly powerful for it's age. My experience is that my GPU is barely being used, but my CPU is getting close to it's limits when render lag starts. I have an extremely bloated scene with 4 monitors and multiple display captures, and a ton of Apps I run during the stream. The number 1 solution to help reduce CPU usage (albeit at at cost - Quality loss), is raising Your CPU preset higher - Settings>output>streaming>cpu usage preset - The higher you go, the less CPU is tasked. Start one higher than where you are now, eg. faster - change to veryfast. If that isn't good enough, up it to superfast and then ultrafast. Again, if you go too high, this will pixilate a little when being pushed a bit, but your render lag will be gone. It will still look way better than tons of dropped frames due to render lag. If none of that helps, lower your resolution. 720 instead of 1080 etc. and 30fps vs 60 fps.

Much thanks for your reply. Although many people said rendering is done on GPU, I still suspect that OBS at least allocated some parts of the rendering work to CPU. Or I could also be that OBS just doesn't provide support for old models of GPU. My case was a little different from yours because I didn't have a streaming session. I also tried lowering the resolution from 1080p to 720, as well as reducing the fps from 60 to 30. But that doesn't help much. Also I looked through the preference panes but it doesn't seem to have any setting related to the rendering things.