Hi Stefan, On Sun, 06 Sep 2020, Stefan Hagen wrote:
> Hello, > > Lauries video(1) email to misc@ encouraged me to take this information > and try to come up with a proposal to enhance the multimedia faq with > information about webcam usage. > > It's the first time I'm working on a faq article and I don't know about > any style guides. I tried to align with the articles already written. > Please educate me about the parts I missed. > > I'm not sure where people working on documentation collaborate. So > I'm trying my luck here on tech@. > > My proposal is online and I'm also inlining it (not as patch for easier > consumption): https://codevoid.de/h/wip_webcamfaq13.html > > I'm sure some parts need refinement / better wording. > > The part I'm mostly unsure about is how to correctly give the user > permissions to the video devices. Most people probably do it the > way I described (doas chmod $USER in .xsession). > > Once it's good enough to get committed, I'll create a proper patch. > > Any thoughts on it? First, thanks for working on this. I think it's a good idea, let's see what other devs say. One quick comment on the "Using a webcam as user" section. Besides adding the chown line on .xsession you can use /etc/X11/xenodm/GiveConsole too (not sure if this is "less preferred" than your method). I have this in mine: if [ -c /dev/video0 ]; then chown $USER /dev/video0 fi Which should be accompanied with an entry on /etc/X11/xenodm/TakeConsole if [ -c /dev/video0 ]; then chown root /dev/video0 fi In any case, the suggestion of a _video group seems cleaner to me, but if it has not been done already I suspect there are good reasons for it (did not dig into the archives, so I'm speculating here). I'll take a deeper look later. Cheers, Paco. > > Thanks in advance, > Stefan > > ---- > > <h2 id="webcams">Using a Webcam</h2> > > <h3>Supported Hardware</h3> > > <p> > Most webcams today work according to the USB Video Class > (UVC) specification, which is supported by the <a > href="https://man.openbsd.org/uvideo";>uvideo(4)</a> device driver and > attaches to the <a href="https://man.openbsd.org/video.4";>video(4)</a> > device. The manpage lists some supported devices, but there is a > good chance that other devices work as well. For example, webcams in > Lenovo Thinkpads laptops do usually work. > > <p> > A supported webcam (or other video device) shows up in <code>dmesg</code> > like this: > > <pre class="cmdbox"> > uvideo0 at uhub0 port 8 configuration 1 interface 0 "Azurewave Integrated > Camera" rev 2.01/69.05 addr 10 > video0 at uvideo0 > uvideo1 at uhub0 port 8 configuration 1 interface 2 "Azurewave Integrated > Camera" rev 2.01/69.05 addr 10 > video1 at uvideo1 > </pre> > > <p> > You see that an <code>uvideo</code> device was detected and has > been attached to <code>video0</code>. This device will be accessible > through <code>/dev/video0</code>. > > <p> > Modern laptops sometimes attach a second video device, which is the > infrared camera for face recognition. The second camera does not produce > a usable video stream. > > <p> > You can find the usable camera with the <a > href="https://man.openbsd.org/video";>video(1)</a> command: > > <pre class="cmdbox"> > $ <b>video -q -f /dev/video0</b> > video device /dev/video0: > encodings: yuy2 > frame sizes (width x height, in pixels) and rates (in frames per second): > 320x180: 30 > 320x240: 30 > 352x288: 30 > 424x240: 30 > 640x360: 30 > 640x480: 30 > 848x480: 20 > 960x540: 15 > 1280x720: 10 > controls: brightness, contrast, saturation, hue, gamma, sharpness, > white_balance_temperature > > $ <b>video -q -f /dev/video1</b> > video: /dev/video1 has no usable YUV encodings > </pre> > > <p> > The usable camera device shows supported resolutions and framerates. > Note that the framerates only apply to the uncompressed YUY2 stream. More > on that in <a href="#recvideo">Recording a webcam stream</a>. > > <h3>Using a webcam as user</h3> > > <p> > To use the webcam as regular user, you need to change the device > permissions. Only root is allowed to access video devices by default. > > <p> > One way of allowing your user to access the video devices is to change > the permissions from <code>~/.xsession</code>. You can configure > <a href="https://man.openbsd.org/doas";>doas(1)</a> to perform > <a href="https://man.openbsd.org/chmod";>chmod(1)</a> as superuser > without asking for a password for your user. > > <p> > Then add the following line to your <code>~/.xsession</code>: > > <pre class="cmdbox"> > doas chown $USER /dev/video0 > </pre> > > <p> > If you're not using <a > href="https://man.openbsd.org/xenodm";>xenodm(1)</a> > and you are starting your X session with > <a href="https://man.openbsd.org/startx";>startx(1)</a>, you can > accomplish the same with > <a href="https://man.openbsd.org/fbtab";>fbtab(5)</a>. > > <p> > Example entry in <code>/etc/fbtab</code>: > > <pre class="cmdbox"> > /dev/ttyC0 0600 /dev/video0 > </pre> > > <h3 id="recvideo">Recording a webcam stream</h3> > > <p> > This section uses <code>ffplay</code> and <code>ffmpeg</code> from > graphics/ffmpeg. To find out what your camera is capable of, run the > following command: > > <pre class="cmdbox"> > $ <b>ffplay -f v4l2 -list_formats all -i /dev/video0</b> > [...] > [video4linux2,v4l2 @ 0x921f8420800] Compressed: mjpeg : MJPEG : 1280x720 > 320x180 320x240 352x288 424x240 640x360 640x480 848x480 960x540 > [video4linux2,v4l2 @ 0x921f8420800] Raw : yuyv422 : YUYV : 640x480 > 320x180 320x240 352x288 424x240 640x360 848x480 960x540 1280x720 > </pre> > > <p> > At the end of the output, you'll find two lines similiar to the two > above. > > <p> > The first line shows resolutions supported in the uncompressed YUYV > format. The frame rates in this format can be very low. > > <p> > The second line shows the supported MJPEG compressed video resolutions, > which deliver much higher framerates (usually 30fps or 60fps). > > <p> > Now try to play the webcam stream. Choose one of the MJPEG resolutions > and run: > > <pre class="cmdbox"> > $ <b>ffplay -f v4l2 -input_format mjpeg -video_size 1280x720 -i > /dev/video0</b> > [...] > Input #0, video4linux2,v4l2, from '/dev/video0':B sq= 0B f=0/0 > Duration: N/A, start: 1599377893.546533, bitrate: N/A > Stream #0:0: Video: mjpeg (Baseline), yuvj422p(pc, > bt470bg/unknown/unknown), 1280x720, 30 fps, 30 tbr, 1000k tbn, 1000k tbc > </pre> > > The webcam stream should be displayed. Ffplay also shows the used > resolution and the framerate (fps) used. > > <p> > If this works, you can go ahead and record the video with ffmpeg: > > <pre class="cmdbox"> > $ <b>ffmpeg -f v4l2 -input_format mjpeg -video_size 1280x720 -i /dev/video0 > ~/video.mkv</b> > </pre> > > End the recording with "q". You have now recorded your stream to file > <code>~/video.mkv</code>. > > <h3>Controlling webcam settings</h3> > > <p> > Webcams usually have brightness, contrast and other controls. > <a href="https://man.openbsd.org/video.1";>Video(1)</a> > allows you to alter these settings. > > <p> > First find out which supported controls your camera has: > > <pre class="cmdbox"> > $ <b>video -c</b> > brightness=128 > contrast=32 > saturation=64 > hue=0 > gamma=120 > sharpness=3 > white_balance_temperature=auto > </pre> > > <p> > You can change for example the brightness setting to 200: > > <pre class="cmdbox"> > $ <b>video brightness=200</b> > brightness: 128 -> 200 > </pre> > > <p> > If you would like to reset all settings to their defaults, you can do so > with: > > <pre class="cmdbox"> > $ <b>video -d</b> > $ <b>video -c</b> > brightness=128 > contrast=32 > saturation=64 > hue=0 > gamma=120 > sharpness=3 > white_balance_temperature=auto > </pre> > > <p> > Some settings, like the <code>white_balance_temperature</code> support > automatic adjustments. You can set them to a fixed value or set them to > "auto", which lets the camera decide and use whatever value it thinks is > best. > > <h3>Access webcam in chromium</h3> > > <p> > Chromium has access to <code>/dev/video</code> by default. To > allow Chromium to access other video devices, you need to add > the device paths to <code>/etc/chromium/unveil.main</code> and > <code>/etc/chromium/unveil.utility_video</code> > > <h3>Access webcam in firefox</h3> > > <p> > Firefox has access to <code>/dev/video</code> and <code>/dev/video0</code> > by default. To allow Firefox to access other video devices, you need to > add the device paths to <code>/etc/firefox/unveil.main</code>. > -- Paco Esteban. 0x5818130B8A6DBC03
