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You'reAGitForNotUsingGit
Asked: 2019-06-17 12:32:26 +0800 CST

Problems recording video from my Logitech C920 webcam

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I'm attempting to record a 1080 @ 30FPS video from a Logitech C920 webcam. Simple, right? Well, apparently not.

First, I tried on my desktop running 16.04 using Ubuntu's built-in Cheese application. The preview streams perfectly fine at 30FPS, but as soon as I start recording, the frame rate drops drastically to probably around ~15FPS (I don't know exactly since Cheese doesn't provide an FPS meter).

Next, I tried again on my desktop running 16.04 using guvcview. Unfortunately, the version in the default repos for 16.04, 2.02, has a bug which causes it to record video as a single still frame. Arghh... so then I installed 2.05 from an unofficial PPA. This solved the aforementioned bug, however, when I go to record video (using H.264 from the camera's hardware encoder) the first second or so of the video records perfectly, but then the frame rate drops to between 3 and 5 FPS.

Finally, to make sure it wasn't just a problem with my desktop, I installed guvcview version 2.05 on my laptop running 18.04, but once again, when I go to record video (using H.264 from the camera's hardware encoder) the first second or so of the video records perfectly, but then the frame rate drops to between 3 and 5 FPS.

So what the heck is going on here? Is this an issue with libuvc compatibility with the Logitech C920? I know it's not an issue of under-powered hardware, as I have a 6-core AMD CPU in my desktop and a quad-core 3rd gen i7 in my laptop.

video webcam logitech guvcview uvc

1 Answers

  1. Best Answer

    I figured out how to make it work with guvcview.

    I found this post which mentioned that the issue was that guvcview was re-encoding the stream from the camera. Why that caused the horrible frame rate drop is a mystery to me, given that my CPU usage was extremely low...

    Anyway, the fix is to tell guvcview to use the raw stream from the camera:

    enter image description here

    Please note that the format you tell the program to re-encode (or not) to is totally separate from the format you tell it to stream from the camera:

    enter image description here

    Also, on another note, it seems that either I have no idea how to tune the huge number of H.264 parameters in guvcview, or that the hardware H.264 encoder in the Logitech C920 is just really not that good. I recorded a 1080p30 clip in MJPEG (which resulted in about 60Mb/s of data) and transcoded it into 10Mb/s H.264 using Veags Pro on my Windows box, and the result was vastly superior to streaming from the webcam directly in H.264, also at 10Mb/s.

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