Building a webcam recorder with VLC, Ion and Ruby

I promised to build a system to let people leave video messages at a party. The requirements were:

• people have to see the stream while it is recorded, so they're sure they are in the video
• the system has to be extremely simple to use, possibly requiring the use of only one keyboard keypress to start and stop recording
• the recorded video have a maximum length, so that we avoid recording when someone forgot to stop the recording after his/her message

After looking at several options, including GStreamer and Ffmpeg, there was no easy solution in sight. And then I took a look at Videolan, also known as VLC. Here's how I got to a working solution. Note however this is a quick hack.

With VLC's WxWidgets interface, it is easy to open a video4linux device (I'm using QuickCam Express II): File > Open Capture Device:



In this dialog, check that the correct device is opened (I open /dev/video0), and things should work as expected: when you click "OK", you see the images captured by your webcam.


In the dialog above, you might have seen the checkbox "Stream/Save". Checking it enables to save the stream from your webcam to a file, the spec of this file being set in the dialog appearing when you click on the Settings Button:


From top to bottom:

1. Check "Play locally", as this shows the stream captured by the webcam on your screen
2. check "File", as this will save the stream coming from the webcam into the filename you enter in the textbox.
3. choose MP4 as "Encapsulated Method". You need to choose this carefully as not all encapsulation methods accept all format. Check the VLC streaming features page for more info.
4. According to the Encapsulation Method you have chosen, choose the right video and audio codec. For MP4 it's respectively mp4v and mpga. If you only want to dump the video, only the video checkbox has to be ticked.

Clicking ok in each dialog will show you the stream in VLC's window, and dump it in the file you entered in the configuration dialog.

Now that it is working with the interface, the next step is to get it working from the command line. As you may have noticed, when you set options in the configuration dialogs above, a text field is filled accordingly. For example, when setting the configuration in the "Save/Stream" options dialog, the top text field has its value set to
<br />:sout=#transcode{vcodec=mp4v,vb=1024,scale=1,acodec=mpga,ab=192,channels=2}:duplicate{dst=display,dst=std{access=file,mux=mp4,dst="/tmp/test.mpg"}}<br />
which contain all configuration option set in the dialog.

And in the "Open Capture Device", the bottom text field has its value set to

v4l:// :v4l-vdev="/dev/video0" :v4l-adev="/dev/dsp" :v4l-norm=3 :v4l-frequency=-1

These configuration strings can be used on the command line when launching vlc. Each v4l corresponds to a long option passed to vlc. :v4l-vdev="/dev/video0" becomes --v4l-vdev /dev/video0 on the command line.

We end up with this command:
<br />vlc --v4l-vdev "/dev/video0" --v4l-norm 3 --sout '#transcode{vcodec=mp4v,vb=1024,scale=1,acodec=mpga,ab=192,channels=2}:duplicate{dst=display,dst=std{access=file,mux=mp4,dst="/tmp/test.mpg"}}<br />


The next step is to start and stop the recording from a script. This is possible thanks to the RC interface offered by vlc. the RC interface, launched by passing the option -I RC to vlc, gives you a command prompt to control VLC. With the option "--rc-host localhost:4444", this command interface is even reachable by telnet on port 4444.

Typing help at the command prompt will give all commands available, but we'll only need:

• add v4l:// to start the recording. It opens the v4l device passed in the options of the command line, and outputs the stream to what we configured on the command line as well: the file and the screen.
• stop to end the recording

Before building an interface on this, I had to correct a little problem: the image displayed was way too dark. In the vlc interface, in Settings > Extended GUI , you have access to Image adjustments, where you can activate and set Hue, Contrast, Brightness, Saturation and Gamma correction. These can be set and activated from the command line with the corresponding option. Here are the options I had to use:

--contrast 1.9 --brightness 1.7  --saturation 2.3

I've had problem sometimes for the options to be taken into account. Going through the vlc extended GUI and enabling the image adjustements usually fixed it.

Building a little interface on this is quite straight-forward. I used Ruby and Tk. The GUI is made of.... 1 button used to start and stop the recording. It is triggered by pressing the "Enter" key. The control GUI also shows how long, in seconds, the person still has before reaching the maximum lenght of the recording.



The script starts VLC with the RC interface and the telnet connections accepted on port 4444. All commands are passed to VLC through the telnet connection. VLC always stores the dumped stream in the same location, and at the end of the recording session, the script moves it over to a definitive location, with a unique name based on the timestamp.

The problem with this setup in a "standard" window manager, is that recording starts, a window is opened to display the image coming in from the camera. this window covers the command unterface, which makes it impossible for the user to simply press on Enter to stop the recording, and the focus is on the vlc output window.

For Ion 3 users, there a quick solution here: split your workspace in two, and make the GUI appear in the left frame, and the vlc output window in the right. What's even cooler is that when the vlc output window is opened when the user starts the recording, the focus stays with the command GUI.

I will assume that you have installed Ion3, and copied the standard config files to ~/.ion3, as explained in the Ion3 documentation.

I created a new user, for which I set Ion3 as the window manager to use. I'm using kdm, so I edit .xsession with this content

exec /usr/local/ion3/bin/ion3

and at log in I choose the "Default" window manager.

When you log in, you get a workspace with one frame. To split it vertically, use Meta+K S. You can bind the key you want to Meta in ~/.ion3/cfg_ion.lua. I set it to Meta4, which is the Windows key on my laptop.

To identify the frame, it is necessary to give them a name. Focus the frame you want to rename, and press Meta+F3. This brings up the Lua code interpreter. Type the following command:

mod_query.query_renameframe(_)

and press "Enter". You are then promted for a name. Give the name app to the left frame, and vlc to the right one.
Ion automatically saves your workspaces when you log out. As the app is running under a specific user, this will not have to be repeated.

To make a window appear in a specific frame is achieved with the defwinprop directive in the user configuration of Ion. To identify the properties of a window, the xprop command can be used, or, even better when using the Ion WM, use the frame context menu (left click on the title bar of the frame, of Meta+M) to get the "Window Info":



Once you have this info, you can configure the GUI window to appear in the left frame.

The class of the command GUI is Webcamrecorder.rb, the instance is webcamrecorder.rb. It should go in the app frame, and focus should go to this window. This gives this configuration line in cfg_user.lua:
<br />defwinprop { class ="Webcamrecorder.rb" , instance = "webcamrecorder.rb" , target = "app", jumpto = true}<br />


The problem with the vlc output window is that it has no class nor instance property set... Only the title is set to "VLC XVideo ouput", which is an identification information not supported by defwinprop.... I set this in the cfg_user.lua file, so that all windows except the control GUI appear in the right frame:

defwinprop { target = "vlc"}

I set the last line of the cfg_user.lua file to

exec('xterm -e /usr/local/bin/webcamrecorder.rb')

to start the webcamrecorder immediately when logging in.

Note that I first wanted to place this in the .xsession file, but it didn't work. Apparently, webcamrecorder.rb has to be started from a terminal, or it won't work. I suspect this is due to the RC interface we request from vlc.

Once you have your solution up, you can clean your Ion bindings to avoid users switching frames, creating workspaces or starting terminals. I also cleaned up cfg_ion.lua to limit the number of modules loaded. I end up with these config files: cfg_ion.lua, cfg_ionws.lua, cfg_menu.lua, cfg_query.lua. Together with the webcamrecorder.rb script, it's all what makes up this quick hack.

Update: Richard took the script and made a GTK version. He posted it in the comments, together with information on how he's using v4l2. I put the script in a file webcamrecordergtk.rb that you can download. Thanks Richard!