Difference between revisions of "video 4 linux 2 notes"
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gst-launch --eos-on-shutdown v4l2src ! ffmpegcolorspace ! jpegenc ! avimux ! filesink location=video.avi | gst-launch --eos-on-shutdown v4l2src ! ffmpegcolorspace ! jpegenc ! avimux ! filesink location=video.avi | ||
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+ | Record with fixed image size and frame rate. | ||
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+ | gst-launch --eos-on-shutdown v4l2src device="/dev/video0" ! video/x-raw-yuv,width=640,height=480 ! ffmpegcolorspace ! jpegenc ! avimux ! filesink location=video.avi | ||
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Revision as of 14:08, 1 January 2013
Contents
- 1 V4L2 -- Video For Linux Version Two
- 1.1 UVC
- 1.2 Gstreamer
- 1.2.1 record two video cameras into side-by-side stereo video
- 1.2.2 record video frames into separate files
- 1.2.3 playback separate files as a video (slideshow)
- 1.2.4 mix two video sources into one (side-by-side)
- 1.2.5 date and time stamps
- 1.2.6 interesting filters
- 1.2.7 gstreamer plugin documentation
- 1.2.8 gstreamer flip video
- 1.2.9 gstreamer fbdevsink "ERROR: Pipeline doesn't want to pause."
- 1.2.10 gstreamer xvimagesink "ERROR: ... Could not initialize Xv output"
- 1.2.11 playback video on framebuffer (/dev/fbdev0)
- 1.3 Capture video and modify settings at the same time
- 1.4 fswebcam
- 2 See also
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
Gstreamer is my favorite command-line tool for handling video.
See also this Gstreamer cheat sheet.
This will display the camera view in a window:
gst-launch v4l2src ! ffmpegcolorspace ! xvimagesink
This will display the camera view in a window with a specified size (320x240):
gst-launch v4l2src ! video/x-raw-yuv,width=320,height=240 ! ffmpegcolorspace ! xvimagesink
Record video stream to a file using Motion JPEG encoding (MJPEG):
gst-launch --eos-on-shutdown v4l2src ! ffmpegcolorspace ! jpegenc ! avimux ! filesink location=video.avi
Record with fixed image size and frame rate.
gst-launch --eos-on-shutdown v4l2src device="/dev/video0" ! video/x-raw-yuv,width=640,height=480 ! ffmpegcolorspace ! jpegenc ! avimux ! filesink location=video.avi
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.
gst-launch v4l2src device=/dev/video0 ! 'video/x-raw-yuv,width=1920,height=1080' ! xvimagesink
This will capture at a higher framerate, but it will undersample the pixels so you will get an effective 320x240 resolution.
gst-launch v4l2src device=/dev/video0 ! 'video/x-raw-yuv,width=640,height=480,framerate=60/1' ! xvimagesink
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.
gst-launch --eos-on-shutdown v4l2src ! ffmpegcolorspace ! tee name=my_videosink ! jpegenc ! avimux ! filesink location=video.avi my_videosink. ! queue ! xvimagesink
Video test pattern:
gst-launch videotestsrc ! ffmpegcolorspace ! xvimagesink
record two video cameras into side-by-side stereo video
gst-launch v4l2src device=/dev/video1 ! videoscale ! ffmpegcolorspace ! video/x-raw-yuv, width=320, height=240 ! videobox border-alpha=0 left=-320 ! videomixer name=mixme ! ffmpegcolorspace ! jpegenc ! avimux ! filesink location=sbs-3d-video.mov v4l2src device=/dev/video2 ! videoscale ! ffmpegcolorspace ! video/x-raw-yuv, width=320, height=240 ! videobox right=-320 ! mixme.
Using mplayer you can play side-by-side stereo video as anaglyphic stereo video.
mplayer -vf stereo3d,scale -idx sbs-3d-video.mov -loop 0
record video frames into separate files
gst-launch --eos-on-shutdown v4l2src device=/dev/video1 ! video/x-raw-yuv,format=\(fourcc\)YUY2,width=640,height=480,framerate=30/1 ! ffmpegcolorspace ! videorate ! video/x-raw-rgb,framerate=30/1 ! ffmpegcolorspace ! pngenc snapshot=false ! multifilesink location="frame%05d.png"
playback separate files as a video (slideshow)
gst-launch multifilesrc location=frame%05d.png ! image/png,framerate=5/1 ! pngdec ! videorate ! video/x-raw-rgb,framerate=5/1 ! ffmpegcolorspace ! xvimagesink
mix two video sources into one (side-by-side)
gst-launch v4l2src device=/dev/video1 ! videoscale ! ffmpegcolorspace ! video/x-raw-yuv, width=320, height=240 ! videobox border-alpha=0 left=-320 ! videomixer name=mix ! ffmpegcolorspace ! xvimagesink v4l2src device=/dev/video2 ! videoscale ! ffmpegcolorspace ! video/x-raw-yuv, width=320, height=240 ! videobox right=-320 ! mix.
date and time stamps
The timeoverlay filter adds the frame buffer time to each video frame. The clockoverlay filter adds the date and time to each video frame.
gst-launch -e v4l2src device=/dev/video1 ! video/x-raw-yuv,format=\(fourcc\)YUY2,width=640,height=480,framerate=30/1 ! ffmpegcolorspace ! timeoverlay shadow=false halignment=right valignment=bottom font-desc="sanserif 10" ypad=5 xpad=5 ! clockoverlay shadow=false halignment=left valignment=bottom time-format="%Y-%m-%d %H:%M:%S" font-desc="sanserif 10" ypad=5 xpad=5 ! videorate ! video/x-raw-rgb,framerate=30/1 ! ffmpegcolorspace ! xvimagesink
interesting filters
fpsdisplaysink
gstreamer plugin documentation
Many Gstreamer plugins lack good documentation. You can find internal descriptions of plugins and their properties by using gst-inspect. For examples:
gst-inspect timeoverlay gst-inspect clockoverlay
gstreamer flip video
This is handy if the camera is mounted upside-down or sideways. Upside-down:
gst-launch v4l2src device=/dev/video0 ! video/x-raw-yuv,width=320,height=240,framerate=30/1 ! videoflip method=clockwise ! xvimagesink
Sideways:
gst-launch v4l2src device=/dev/video1 ! video/x-raw-yuv,width=320,height=240,framerate=30/1 ! videoflip method=clockwise ! xvimagesink # or gst-launch v4l2src device=/dev/video1 ! video/x-raw-yuv,width=320,height=240,framerate=30/1 ! videoflip method=counterclockwise ! xvimagesink
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.
$ gst-launch videotestsrc ! ffmpegcolorspace ! fbdevsink Setting pipeline to PAUSED ... ERROR: Pipeline doesn't want to pause. Setting pipeline to NULL ... Freeing pipeline ...
gstreamer xvimagesink "ERROR: ... Could not initialize Xv output"
This happens if your X11 installation does not support Xv. This is a common problem when working with a virtual machine. Try using ximagesink instead of xvimagesink.
playback video on framebuffer (/dev/fbdev0)
sudo gst-launch uridecodebin uri=file:///home/noah/Videos/ct_scan_sample.flv ! ffmpegcolorspace ! fbdevsink
You can also use mplayer to play video on a framebuffer device. Be sure to specify fbdev2 if you want color.
sudo mplayer -vo fbdev2 ct_scan_sample.flv
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