Screencasts - digital movies with the desktop as a backdrop, the mouse as the protagonist and a voiceover - have become an integral part of electronic learning and form the basis of the computer-based training industry. As bandwidth becomes affordable and video-sharing websites start popping up, there's a huge influx of free and open source tools.

Not all tools follow the same methodology of capturing activity on your screen. Some rely on desktop sharing services such as VNC, some take a series of screenshots in quick succession and stitch them together into a video.

Some give you the option to select an output format, and some will spew the video in patent-free formats only. Using these tools you can screencast your complete desktop or a particular window. Some enable you to narrate audio along with your videos and others don't.

Which to choose? Read on for our group test of the best screencasting apps available for Linux...

How we tested

Support for audio recording and output format are two massively important factors for screencasting apps. While patent-free formats are good, they aren't very useful for uploading the screencast to a video sharing website.

The size of the output video wasn't factored in, because it's difficult to duplicate the same actions, and keep the length of the video and narrations constant across various apps. In our non-scientific observations there wasn't much difference in the output video irrespective of the app used as long as we used the same codec.

All the applications were tested on two computers - a 1.4GHz Celeron laptop with 1 GB RAM, and an Intel dual-core desktop machine. The apps were run from their GUI and CLI to capture screencasts on KDE and Gnome desktops, including fancy ones such as Compiz.

RecordMyDesktop

RecordMyDesktop is an open source screencasting tool that produces videos in the open source Ogg format. It's written in C and offers flexibility and control to appeal to new and experienced screencasters.

There are Python front-ends for RecordMyDesktop for KDE and Gnome, both of which show a live preview of the desktop that you can use to select the area of the desktop that you want to capture and give you plenty of options to customise the captures.

For example, if you're demoing a graphical app that has lots of graphical elements with tooltips, you can choose not to capture the tooltips. If you've selected a small area you can ask RecordMyDesktop to follow your mouse, which keeps the size of the screencast fixed but tracks your mouse movement as you move around the desktop. You can also choose to disable capturing the cursor at all.

Configurable capture

By default the app captures at 15fps, which should work for most screencasts, but you can change it if the default doesn't work for you.

Also by default. RecordMyDesktop, encodes the video after it's done capturing, which requires temporary storage space to store the captured images. If you don't have the space, you can encode on the fly, which requires a lot of processing power. Another option designed to make RecordMyDesktop work on low-power boxes is the ability to disable compression, which reduces overheads at the expense of taking more disk space.

Finally there's the option to enable quick subsampling, which again helps ease the load on the processor - just use it as a last-resort, as it might add blur to the videos. We used RecordMyDesktop on a 1.4GHz Celeron laptop with 1GB RAM and a dual-core Intel desktop, and it worked just as well on both machines.

RecordMyDesktop can directly interface with the ALSA or OSS sound system, or can connect to the recording port via the Jack audio server. You can specify the number of channels and the frequency that will be used to encode the audio captures. By default both video and audio captures are set at the best quality possible, but you can reduce this to decrease the output size of the final encoded video.

If you don't want to start the capture immediately, you can delay it by several seconds, minutes or even hours.
Our verdict: Stable app with good control and simple interface. Only outputs in Ogg. 8/10.