This post is in english / Dieser Artikel ist auf Englisch, weil er nicht nur für die deutschen Pidgin-Nutzer hilfreich sein soll.

Recently, Google+ and Facebook introduced video chatting. While video chatting is not a new technology at all, I noticed that I never really tried it except for a few experiments. Therefore, I wanted to set up video chatting between two Linux computers, using only free and open source software.

I decided to use XMPP (Jabber) instead of SIP for this, due to my bad experiences with SIP and NAT / packet filters. Also, both users already use XMPP to communicate.

As you can see on the Wikipedia page about Jingle, the video chat protocol extension for XMPP, quite a few clients say they support Jingle. I decided to try it with Pidgin in version 2.9.0 (it has support for Jingle since 2.6.0).

Camera

Linux provides plug & play support for UVC cameras (enable the USB_VIDEO_CLASS kernel option, module is called uvcvideo). One camera which got good reviews on Amazon and reportedly works on Linux is the Logitech C270 USB HD Webcam. I bought it for about 22 € and it works just fine on my machines with Linux 2.6.39.3.

Update: The Logitech C270 USB HD Webcam does not work fine on my computer: The usb audio driver has a bug which causes the audio of the C270’s microphone to stutter occasionally. This affects both models I bought, which is why I returned the camera.

After plugging it in, you can use MPlayer to check if your camera is working:

$ mplayer -v tv:// -tv device=/dev/video0:driver=v4l2

To tune some parameters (contrast, light, …), use the uvcdynctrl tool. The most important setting for most cameras is the Auto Exposure setting: When activated, the camera will take a long time for exposure, which results in a frame rate of 5 fps instead of 30 fps (the picture quality is much better, though). So be sure to change the Auto Exposure setting.

Installing packages

Pidgin’s implementation of Jingle uses Farsight and GStreamer. I installed the following packages on both systems:

• gstreamer-tools (0.10.35-1)
• gstreamer0.10-alsa (0.10.35-1)
• gstreamer0.10-ffmpeg (1:0.10.11-4.1)
• gstreamer0.10-nice (0.1.0-2)
• gstreamer0.10-plugins-bad (0.10.22-2)
• gstreamer0.10-plugins-base (0.10.35-1)
• gstreamer0.10-plugins-good (0.10.30-1)
• gstreamer0.10-plugins-ugly (0.10.18-1)
• gstreamer0.10-pulseaudio (0.10.30-1)
• gstreamer0.10-tools (0.10.35-1)
• gstreamer0.10-x (0.10.35-1)
• gstreamer0.10-x264 (0.10.18-0.0)
• libgstreamer-plugins-base0.10-0 (0.10.35-1)
• libgstreamer-plugins-base0.10-dev (0.10.35-1)
• libgstreamer0.10-0 (0.10.35-1)
• libgstreamer0.10-dev (0.10.35-1)

To verify that your camera is also working in GStreamer, use the following command:

$ gst-launch v4l2src ! xvimagesink

Be sure to test this multiple times. While testing, my buddy ran into a bug, where only the first invocation works on the ThinkPad integrated camera. The patch in that bugreport fixed the problem for him (apply it to the gst-plugins-good0.10 source package).

Pidgin

In Pidgin, first configure your network settings properly. If you (or your buddy) are behind an IPv4 NAT, go to Tools → Preferences → Network and enter stunserver.org as STUN server. Afterwards, configure a port range and enable these ports in your packet filter, if you use a packet filter.

For IPv6 (which Pidgin uses, if available), no further setup is required.

Afterwards, you need to configure your Voice/Video settings (it did not work with various symptoms unless both buddys make specific settings here). Enable the Voice/Video settings plugin in the Tools → Plugins dialog. Then press Configure Plugin and make the following settings:

• Audio → Input → PulseAudio → Webcam C270 Analog Mono
• Video → Output → Plugin → X Window System (XV) → Intel Textured Video
• Video → Input → Plugin → Video4Linux2 → UVC Camera

Please note that all of these settings are important and video chat did not work for us unless we configured all of them.

Now (or after a restart of Pidgin) you should be able to chose Conversation → Media → Audio/Video call in any conversation window with your buddys. This option is disabled if the buddy’s computer / XMPP client does not support video chat.

Codecs

By default, Farsight uses the Theora video codec and Speex audio codec with a relatively high bitrate. I decided I want to use less bandwidth to still have some bandwidth left for other things and to avoid lags.

To configure which codecs are used, create ~/.purple/fs-codec.conf and copy your settings from /usr/share/farsight2/0.0/fsrtpconference/default-codec-preferences, then modify them. For example, to disable Speex, add id=-1 in the SPEEX sections.

To change the bitrate of Theora, create ~/.purple/fs-element.conf and add the following contents:

[theoraenc]
bitrate=210

This resulted in a total bandwidth of about 300 kbit/s (for video and audio).

Voice/Video with different clients

We also tested Gajim and Psi. With Pidgin/Psi, we were able to do voice calls, but no video. With Pidgin/Gajim, we were unable to establish neither voice calls nor video calls.

Conclusion

Video chatting with free and open source software (FOSS) does work. Setting it up, however, is a rather unpleasant experience, which is why I wrote this article. The error reporting by the Pidgin, Farsight and GStreamer combination is horrible. While finding out how to get this to work, we always ended up with open video chat windows where the video just stayed black and the audio was silent. Pidgin did not display any error messages or hints on what was wrong. Even the debug window of Pidgin did not provide any clues.

It is therefore totally understandable why people could be excited about Google+ or Facebook video chatting which reportedly just work. Hopefully, we can improve the video chat situation in FOSS to just work out of the box :).