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Q&A

With a V4L2-compatible webcam, how to see its video feed for the purpose of adjusting aiming?

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I have ordered (but am still waiting for it to arrive) a USB-connected webcam that is supposed to be V4L2 compatible.

Once it arrives, I'm obviously going to want to mount it such that it provides a reasonable picture with minimal ongoing adjustments. I imagine that the easiest way to do so is to simply run some application that shows me what the camera is seeing, and then adjust the camera as needed to get a good result.

The system in question is currently running Debian 10/Buster, but upgrading to 11/Bullseye is on my to-do list, so a solution should ideally work with both of those, preferably without having to download and install out-of-repository applications on either (so any tools suggested should be in both the buster and bullseye Debian repositories).

I found qv4l2 ("test bench application for video4linux devices") which looks somewhat promising for making adjustments, but I haven't found anything that will let me actually see what the webcam is seeing.

How can I accomplish the latter?

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2 comment threads

Expected use cases (2 comments)
Green playback button? (2 comments)

1 answer

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I routinely use MPV for that.

mpv --profile=low-latency --untimed av://v4l2:/dev/video0

You may need to try other devices, as listed by ls /dev/video*.

Thanks to Canina for suggesting the two --options, necessary to avoid latency.

I also found Arch Linux: Webcam setup: Applications, which lists several alternatives, such as Xawtv, VLC and Mplayer. Ffmpeg is also listed there, but it does not fit the requirements of this question because apparently it cannot display the feed at the same time it records.

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sudo usermod -a -G video $(whoami) && sudo -u $(whoami) mpv --profile=low-latency --untimed (3 comments)

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