Robert Edmonds on Nostr: So I noticed an interesting difference between the Elgato Facecam (0fd9:0078) and the ...
So I noticed an interesting difference between the Elgato Facecam (0fd9:0078) and the Razer Kiyo Pro (1532:0e05). Both webcams that support 1920x1080@60, both updated to the latest firmwares from the manufacturers.
I checked the frame capture inter-arrival times on both cameras, using both the kernel-reported timestamps as well as re-timestamping the frame in userspace once each frame is dequeued from the kernel. It bounces around by a few milliseconds in the first 3-5 seconds after capture start on both cameras, but after that they stabilize and the Elgato camera produces a frame every 16.666 ms or so +/- a few microseconds and averages 60.00 fps. The Razer, on the other hand, has an interesting jitter pattern. More often than not frames are coming in every ~16.6 ms, but a lot of frames are arriving multiple milliseconds higher or lower than that. And the long-term average fps that it's putting out is 59.94 fps, not 60.00, which is very suspicious because 59.94 is the old NTSC field rate.
Here's a one second sample of inter-arrival times (ms) from the Elgato, average 16.6665, range 16.647–16.691. This is nice. You can vsync to this without a queue.
16.654
16.668
16.659
16.665
16.672
16.678
16.659
16.656
16.676
16.668
16.686
16.657
16.664
16.655
16.670
16.672
16.670
16.654
16.652
16.682
16.665
16.682
16.662
16.678
16.648
16.670
16.679
16.660
16.651
16.690
16.647
16.668
16.669
16.668
16.670
16.669
16.677
16.657
16.657
16.667
16.676
16.668
16.656
16.671
16.671
16.671
16.658
16.691
16.653
16.656
16.673
16.655
16.683
16.656
16.672
16.669
16.653
16.682
16.656
16.669
And here's a one second sample of inter-arrival times from the Razer, average 16.70345, range 11.875–21.317. If you're occasionally waiting 19 or 21 ms for a frame you'd miss vsyncs unless you build up a queue to smooth out the jitter.
16.625
19.002
16.625
16.626
16.624
16.626
16.625
16.625
16.625
16.626
16.624
16.626
16.625
19.001
14.250
16.625
19.000
11.875
19.001
18.999
11.875
19.001
19.000
14.251
16.625
19.000
16.625
14.250
21.317
14.310
14.250
18.999
18.942
14.309
16.625
16.566
14.309
16.626
16.624
19.002
14.250
19.000
16.626
14.249
16.625
19.002
19.000
14.250
16.625
19.000
14.250
16.626
19.000
16.626
14.250
19.000
14.250
16.625
19.000
14.192
This is unfortunate that the Razer has worse frame pacing because it seems to put out a better looking image than the Elgato.
I checked the frame capture inter-arrival times on both cameras, using both the kernel-reported timestamps as well as re-timestamping the frame in userspace once each frame is dequeued from the kernel. It bounces around by a few milliseconds in the first 3-5 seconds after capture start on both cameras, but after that they stabilize and the Elgato camera produces a frame every 16.666 ms or so +/- a few microseconds and averages 60.00 fps. The Razer, on the other hand, has an interesting jitter pattern. More often than not frames are coming in every ~16.6 ms, but a lot of frames are arriving multiple milliseconds higher or lower than that. And the long-term average fps that it's putting out is 59.94 fps, not 60.00, which is very suspicious because 59.94 is the old NTSC field rate.
Here's a one second sample of inter-arrival times (ms) from the Elgato, average 16.6665, range 16.647–16.691. This is nice. You can vsync to this without a queue.
16.654
16.668
16.659
16.665
16.672
16.678
16.659
16.656
16.676
16.668
16.686
16.657
16.664
16.655
16.670
16.672
16.670
16.654
16.652
16.682
16.665
16.682
16.662
16.678
16.648
16.670
16.679
16.660
16.651
16.690
16.647
16.668
16.669
16.668
16.670
16.669
16.677
16.657
16.657
16.667
16.676
16.668
16.656
16.671
16.671
16.671
16.658
16.691
16.653
16.656
16.673
16.655
16.683
16.656
16.672
16.669
16.653
16.682
16.656
16.669
And here's a one second sample of inter-arrival times from the Razer, average 16.70345, range 11.875–21.317. If you're occasionally waiting 19 or 21 ms for a frame you'd miss vsyncs unless you build up a queue to smooth out the jitter.
16.625
19.002
16.625
16.626
16.624
16.626
16.625
16.625
16.625
16.626
16.624
16.626
16.625
19.001
14.250
16.625
19.000
11.875
19.001
18.999
11.875
19.001
19.000
14.251
16.625
19.000
16.625
14.250
21.317
14.310
14.250
18.999
18.942
14.309
16.625
16.566
14.309
16.626
16.624
19.002
14.250
19.000
16.626
14.249
16.625
19.002
19.000
14.250
16.625
19.000
14.250
16.626
19.000
16.626
14.250
19.000
14.250
16.625
19.000
14.192
This is unfortunate that the Razer has worse frame pacing because it seems to put out a better looking image than the Elgato.