Difference between revisions of "video 4 linux 2 notes"

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[[Category:Engineering]]
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[[Category: Engineering]]
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[[Category: Imaging]]
  
 
= V4L2 -- Video For Linux Version Two =  
 
= V4L2 -- Video For Linux Version Two =  
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== Gstreamer ==
 
== Gstreamer ==
  
Gstreamer is my favorite command-line tool for handling video.
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See [[gstreamer]].
 
 
This will display the camera view in a window:
 
<pre>
 
gst-launch v4l2src ! ffmpegcolorspace ! xvimagesink
 
</pre>
 
 
 
This will display the camera view in a window with a specified size (320x240):
 
<pre>
 
gst-launch v4l2src ! video/x-raw-yuv,width=320,height=240 ! ffmpegcolorspace ! xvimagesink
 
</pre>
 
 
 
Record video stream to a file using Motion JPEG encoding (MJPEG):
 
<pre>
 
gst-launch --eos-on-shutdown v4l2src ! ffmpegcolorspace ! jpegenc ! avimux ! filesink location=video.avi
 
</pre>
 
 
 
1920x1080: This will have a low frame-rate since it will essentially max-out the USB bandwidth. It's useful for capturing individual frames without compression.
 
<pre>
 
gst-launch v4l2src device=/dev/video0 ! 'video/x-raw-yuv,width=1920,height=1080' ! xvimagesink
 
</pre>
 
 
 
This will capture at a higher framerate, but it will undersample the pixels so you will get an effective 320x240 resolution.
 
<pre>
 
gst-launch v4l2src device=/dev/video0 ! 'video/x-raw-yuv,width=640,height=480,framerate=60/1' ! xvimagesink
 
</pre>
 
 
 
Record video and display the stream at the same time requires '''tee''' to split the stream. Notice how the '''name''' parameter of '''tee''' refers to a label defined at the end of the command-line. Also notice how '''queue''' is necessary so that '''xvimagesink''' will run in parallel with the '''filesink'''. Without this you would record video but you would see a window with a single frozen frame of video.
 
<pre>
 
gst-launch --eos-on-shutdown v4l2src ! ffmpegcolorspace ! tee name=my_videosink ! jpegenc ! avimux ! filesink location=video.avi my_videosink. ! queue ! xvimagesink
 
</pre>
 
 
 
Video test pattern:
 
<pre>
 
gst-launch -v videotestsrc ! ffmpegcolorspace ! xvimagesink
 
</pre>
 
 
 
=== gstreamer fbdevsink "ERROR: Pipeline doesn't want to pause." ===
 
 
 
If you are trying to use the framebuffer device for video playback then you may get an error like the one below. This is a permissions problem. Try adding '''sudo''' in front of the pipeline, or run the command as root.
 
 
 
<pre>
 
$ gst-launch videotestsrc ! ffmpegcolorspace ! fbdevsink
 
Setting pipeline to PAUSED ...
 
ERROR: Pipeline doesn't want to pause.
 
Setting pipeline to NULL ...
 
Freeing pipeline ...
 
</pre>
 
 
 
=== playback video on framebuffer (/dev/fbdev0) ===
 
 
 
<pre>
 
sudo gst-launch uridecodebin uri=file:///home/noah/Videos/ct_scan_sample.flv ! ffmpegcolorspace ! fbdevsink
 
</pre>
 
 
 
You can also use '''mplayer''' to play video on a framebuffer device. Be sure to specify '''fbdev2''' if you want color.
 
<pre>
 
sudo mplayer -vo fbdev2 ct_scan_sample.flv
 
</pre>
 
  
 
== Capture video and modify settings at the same time ==
 
== Capture video and modify settings at the same time ==

Latest revision as of 22:44, 23 June 2014


V4L2 -- Video For Linux Version Two

UVC

For a list of cameras that support UVC see the official Linux UVC site. Full UVC support in Linux:

I have been using a Logitech HD Pro Webcam C910, USB Device ID: 046d:0821, for my tests.

Gstreamer

See gstreamer.

Capture video and modify settings at the same time

Start `guvcview` with the --control_only option to display a GUI dialog to edit camera settings. This will work while another video display or capture application is already running.

guvcview --control_only --device=/dev/video0

fswebcam

`fswebcam` is a small and simple tool for grabbing still images from a camera. The world needs more apps like this. It can grab a single image or grab sequences of images in a loop. It can save images to a file or pipe them to stdout.

fswebcam --png --save fswebcam-test.png


Common UVC patterns with `uvcdynctrl`

apt-get install uvcdynctrl
uvcdynctrl --device=/dev/video1 --clist
uvcdynctrl --device=/dev/video1 --get='Focus, Auto'
uvcdynctrl --device=/dev/video1 --set='Focus, Auto' 0
uvcdynctrl --device=/dev/video1 --set='Focus (absolute)' 20

See also