Monitor a Webcam
Contents
Plug in your webcam
Before you plug in your webcam, try the following command at a console:
ls /dev/video*
I don't have any video devices on my system so I get:
No such file or directory
Now Plug in your webcam
List the USB devices using
lsusb
You should see something like this.
Bus 001 Device 005: ID 1415:2000 Nam Tai E&E Products Ltd. or OmniVision Technologies, Inc. Sony Playstation Eye Bus 001 Device 003: ID 0424:ec00 Standard Microsystems Corp. Bus 001 Device 004: ID 05e3:0660 Genesys Logic, Inc. USB 2.0 Hub Bus 001 Device 002: ID 0424:9512 Standard Microsystems Corp. Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 001 Device 005: shows a USB Playstation Eye has been recognised.
Repeat the first command and make a note of the new devices names.
ls /dev/video*
Now we get
/dev/video0
This means the device has automatically been detected and recognised by the system. It doesn't mean you have a means of watching the video data, not yet.
Video Tools
First we're going to need some video capture tools
MPlayer is capable of displaying a webcam video stream.
MEncoder can record from a webcam to video files. The companion to MPlayer,
FFmpeg is a cross-platform audio/video recording, conversion and streaming application.
sudo apt-get install mplayer mencoder ffmpeg
Wait patiently for the programmes and the dependencies to be installed.
User Permissions
List the current users who can access video devices, using
cat /etc/group | grep video
video:x:44
Modify the group to add your user
gpasswd -a [user] video
replace [user] with your username eg. jack
video:x:44:jack
Group changes only change when you next login, so logout and log back in.
View a live feed
mplayer tv:///dev/video0
when viewing this via a remote SSH connection you'll need your RPi display on to see the output!
Use Ctrl-C to terminate the feed.
I noticed that there were a large number of dropped frames reported by mplayer.
MPlayer interrupted by signal 2 in module: filter_video v4l2: ioctl set mute failed: Invalid argument v4l2: 416 frames successfully processed, 1225 frames dropped
This is probably related to the RPi limited CPU when processing my 640x480 images.
Save video to a file
ffmpeg -f video4linux2 -s vga -i /dev/video0 out.mpg
You may need to experiment with the format -f video4linux2 or the size -s vga to match your webcam.
Remember to press 'q' to stop the process
Convert the video format
mencoder out.mpg -ovc lavc -lavcopts vcodec=mpeg4 -o out2.avi
This converts the mpeg2 data to mpeg4.
Note, transcoding video formats on your RPi will be slow.
Now you can playback using the hardware accelerated player omxplayer, assuming you have it installed.
omxplayer out2.avi
Troubleshooting
- USB Camera not detected.
- The RPi has limited capability to supply power to USB devices, try again using a powered USB hub.
- Search google to check if your webcam is support by linux.[1]
Tested
This page has been tested on the following RPi build standards
Linux raspberrypi 3.1.9+ #95 PREEMPT Thu May 31 13:21:40 BST 2012 armv6l GNU/Linux
