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UVC webcams dropping input frames?
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AlanZ  
#1 Posted : Saturday, January 7, 2017 8:31:23 PM(UTC)
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I have just noticed that any of my webcams that use the Windows USB Video Camera driver (notebook's camera, Logitech c930e and c925e), according to Vmix statistics are showing numbers for source dropped that increment by about 10 per second.

Webcams that use the Logitech driver are not affected.

Any idea what's going on here?
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AlanZ  
#2 Posted : Sunday, January 8, 2017 1:01:57 PM(UTC)
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Here's a screen capture showing the UVC camera's source dropped incrementing, while the Logitech driver stays stable.
Any ideas?
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AlanZ  
#3 Posted : Sunday, January 8, 2017 4:31:31 PM(UTC)
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It looks like my problem was that when defining the input, I was using video format "Default"
Switching to video format "MJPG" solved the problem for the UVC cameras.

Alternately, checking the "Use VMR" box and selecting "Default" also seems to work.

Oh, I did run into a related issue... I had most of the lights in the room turned off for some of my testing, and the camera evidently slowed its shutter speed, causing dropped frames. Turn up the lights, dropped frames ended.

So, which approach is better with UVC on Windows 10?
"MJPG" with no VMR
or "Default" with VMR

????
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doggy  
#4 Posted : Sunday, January 8, 2017 4:40:15 PM(UTC)
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by coincidence I read (and tried) this today, maybe is of some help ?

webcamsetting
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thanks 1 user thanked doggy for this useful post.
Rottenham on 2/10/2017(UTC)
mjgraves  
#5 Posted : Tuesday, January 10, 2017 12:15:46 PM(UTC)
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The Logitech proprietary driver associated with the C910/C920 is rather famous for being a CPU hog. In particular, the Right Light and auto-focus features can tax a host system. The OBS/Xsplit community have good guidance on switching to using the UVC driver.

Beyond that, you may have issues with USB bandwidth. Using "Default" video encoding usually results in YUY2, which being uncompressed, will consume most of a USB 2.0 link. That means you can only have one camera per USB 2.0 bus, and not shared with other high bandwidth stuff.

If you change the video encoding to MJPEG you reduce the data over the USB bus by 10x. That gives you a lot more flexibility to combine USB devices without getting into bus bandwidth problems.

If you change the video encoding to H264 the data rate from the camera is even less, but you end up with a couple of seconds of latency since H264 is a Long-GOP based compression scheme.
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AlanZ  
#6 Posted : Tuesday, January 10, 2017 10:22:16 PM(UTC)
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Mjgraves,

To be clear, the issue I was having was not with the Logitech drivers, it was with any cameras (Logitech c930e, c925 or the notebook's built in webcam) that use the UVC driver.

I don't put more than one webcam on a USB channel.

So the question remains, purely from an image quality standpoint... am I better off using MJPG with the newer vMix video system, or using VMR with the default format?

Thanks.
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mjgraves  
#7 Posted : Wednesday, January 11, 2017 2:30:04 PM(UTC)
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According to Martin:

"VMR should not be used unless instructed to do so by support, it is used for diagnosing some issues."

Since dropping frames is generally related to USB bandwidth, I suggest switching to MJPEG encoding.
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AlanZ  
#8 Posted : Wednesday, January 11, 2017 2:32:23 PM(UTC)
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Sounds like a fine plan... that's what I've done
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