HowdoesLinuxdetectyourwebcam?

fswebcam, ffmpeg, MPlayer, and VLC

There are a few command line tools that will let you take a picture using your webcam. I&＃39;ve tried three different tools and found that I liked fswebcam the most, but I&＃39;ve listed all of the options here:

Note that you might need to change your device from /dev/video0 to perhaps /dev/video1! Check the above section to see what webcam is detected.

ffmpeg

ffmpeg -f video4linux2 -i /dev/video0 -vframes 1 test.jpg
ffmpeg -f video4linux2 -s 640x480 -i /dev/video1 -vframes 1 /home/stephen/webcamphotos/$(date &＃43;\%Y\%m\%d\%H\%M).jpg

• ffmpeg man page
• ffmpeg documentation

fswebcam

fswebcam -d /dev/video0 -r 640x480 --jpeg 85 -F 5 test.jpg


This uses a compression factor of 85 (good tradeoff of quality/size) and captures 5 frames (for less noise in image).

• fswebcam man page

MPlayer

mplayer tv:// -tv driver&＃61;v4l2:device&＃61;/dev/video0:width&＃61;640:height&＃61;480 -frames 3 -vo jpeg

• MPlayer documentation
• archLinux article on MPlayer

VLC

vlc -I dummy v4l2:///dev/video0 --video-filter scene --no-audio --scene-path /home/stoppal/test --scene-prefix image_prefix --scene-format png vlc://quit --run-time&＃61;1

Some notes about the Logitech Quickcam Pro 9000

If you are using the Logitech Quickcam Pro 9000 it has an advertised maximum resolution of 1600x1200. Let&＃39;s try to run that with fswebcam.

stephen&＃64;ubuntu:~$ fswebcam -d /dev/video1 -r 1600x1200 --jpeg 85 -F 5 /home/stephen/webcamphotos/$(date &＃43;\%Y\%m\%d\%H\%M).jpeg
--- Opening /dev/video1...
Trying source module v4l2...
/dev/video1 opened.
No input was specified, using the first.
Adjusting resolution from 1600x1200 to 960x720.
--- Capturing 5 frames...
Captured 5 frames in 0.40 seconds. (12 fps)
--- Processing captured image...
Setting output format to JPEG, quality 85
Writing JPEG image to ~/home/stephen/webcamphotos/201304051633.jpeg.


Wait a second! Why did it adjust the resolution to 960x720?

It turns out we need to force it to use a YUYV palette instead of the default

stephen&＃64;ubuntu:~$ fswebcam -d /dev/video1 -p YUYV -r 1600x1200 --jpeg 85 -F 5 /home/stephen/webcamphotos/$(date &＃43;\%Y\%m\%d\%H\%M).jpeg

Configure crontab (make a cronjob) to take a picture every minute or hour

Crontab is a popular *nix utility that executes a command on a user defined interval. Maybe you just want to take a picture every minute, or maybe you want to shutdown your computer Monday through Friday at 10pm. Or maybe you want to run some scripts that backup your data once every 3 months. If you want to run multiple commands you can do so by chaining them with the && keyword, but it&＃39;s also sometimes worth making a bash script (or maybe a simple Python/Perl/Ruby script) that gets executed as part of the cronjob.

To view the current cron jobs for the current user, type crontab -e. To view the current cron jobs for the super user, type sudo crontab -e.

Here are some cronjobs I have set up:

# To take a picture every minute
# */1 * * * * streamer -f jpeg -s 1024x768 -o /home/stephen/timelap/$(date &＃43;\%m\%d\%k\%M).jpeg# To take a picture every hour on the 15 minute mark using a different tool
# 15 * * * * fswebcam -r 1024x768 --jpeg 85 -D 4 -F 10 /home/stephen/webcamphotos/$(date &＃43;\%Y\%m\%d\%k\%M).jpeg# Take a picture and upload it to the webserver every hour
&＃64;hourly bash /home/stephen/scripts/take_photo_and_push.sh

The last cronjob calls a bash script that looks like this:

#!/bin/bash
#Take a picture, then push it to a remote webserver#Take a photo
fswebcam -d /dev/video1 -p YUYV -r 1600x1200 --jpeg 85 -D 2 -F 15 /home/stephen/webcamphotos/$(date &＃43;\%Y\%m\%d\%H\%M).jpeg#Navigate to the directory
cd /home/stephen/webcamphotos/#Find the most recent jpeg
NEW_JPEG&＃61;$(ls -t | grep &＃39;\>.jpeg?s=#39; | head -1)#Push it to the remote webserver
scp /home/stephen/webcamphotos/$NEW_JPEG stephen&＃64;netinstructions.com:/home/stephen/netinstructions.com/homeserver/latest.jpeg

For more information on cronjobs and crontab, take a look at this guide.

If you want to view any logs for the the cron job you can view the logs by typing:

$ grep CRON /var/log/syslog


Viewing/Transferring the Pictures

Okay, so you found a command line utility that takes pictures, and perhaps a cronjob that runs that command every 5 minutes or 10 minutes or every hour or once a day, but how do you look at the picture?

There are a couple of ways of doing this. If you&＃39;re using the desktop version of Ubuntu (with a nice graphical user interface) you just double click on the photo. For the rest of us who are SSH&＃39;ing in to a remote machine or are using the server version of Ubuntu or some other Linx distro, we have a few options:

• FileZilla to grab the files and transfer them to our local machines
• If you have a web server (Apache, ngnix, or something else) on the server, move the file to the web directory
• SCP the file to a remote web server. For example, I have a few websites (such as this one) hosted by Dreamhost, and they provide shell access

The command to securely transfer a file on one machine to another looks like this:

scp /home/stephen/webcamphotos/$NEW_JPEG stephen&＃64;netinstructions.com:/home/stephen/netinstructions.com/homeserver/latest.jpeg


Good luck!