Answer of FAQ

How do I record OpenGL and 3D applications? (with hardware accelerated performance)
How to succeed:

Please use the OpenGL-capable mode of DemoRecorder. ( see below for instructions )

It records the main desktop ( a selectable rectangular area of it, to be more exact ) and it works well with hardware-accelerated OpenGL.

Although this feature is not yet officially released it works quite well and it is already contained in the normal install package. Some of my customers already use this mode in a production environment.

If you need help with this mode or if you experience problems with it, please tell me by email and I will help you.


Here is one example recorded with that mode and exported to avi format:
(this is a recording of the game "glmaze" which is an OpenGL application and a good test-case for OpenGL recording.)


Currently, this recording mode requires the X-Server to be configured for 24bit TrueColor.
(Some Linux distributions use 16-bit TrueColor as the default and that won't work. If the X-Server config does not meet the required 24-bit TrueColor then DemoRecorder will only record the initial frame but no frames thereafter, so you'll get a still image instead of a video.)

You can check your X-Server config by entering the following command into a shell window:


...and looking at the output: Here are the things to look for in the output of "xdpyinfo" ( [...] indicates omitted parts, highlighted stuff indicates relevant info ):

screen #0:
root window id: 0x1a6
depth of root window: 24 planes <-- "24" here indicates 24 bit
number of colormaps: minimum 1, maximum 1
number of visuals: 120
default visual id: 0x21 <-- this may be a different number on your system
 visual id: 0x21 <-- this is the same number as above
 class: TrueColor <-- indicates "TrueColor"
 depth: 24 planes <-- "24" here indicates 24 bit
 available colormap entries: 256 per subfield
 red, green, blue masks: 0xff0000, 0xff00, 0xff
 significant bits in color specification: 8 bits

How to use the OpenGL-capable mode of DemoRecorder


  1. Start it from a shell window as follows (please replace "yourrecording" with the name where you want to store the recording)
    demorec --opengl-hw --out ~/demorec/yourrecording
    (There are options to fine-tune it, cf the output of "demorec --help" )

  2. Select the area to be recorded ( drag the corners of the red rectangle ),
  3. Press the record button ( the circular red button in the small tuerquois rectangle ),
  4. do your presentation or demo,
  5. when you are finished, press the stop button ( the black square button )
  6. To close the recording-application, please press the X-shaped button.


Exporting works the same as with the other recording engine, e.g.

demorec-to-avi --output-bitrate 6000 ~/demorec/yourrecording ~/demorec/yourrecording.avi

When exporting to FLV and then viewing it in the Flashplayer of your webbrowser (which has to be done through a webserver) please note that the Flash player ( at least under Linux) has some performance problems and is therefore dropping frames if a moving 3D scene is played back. So the Flash player cannot keep pace with the performance that DemoRecorder is capable at recording.

So, for active 3D scenes I recommend the AVI or MPEG format because players for these formats are usually optimized for the case of each part of each frame being different from the pervious frame. For AVI and MPEG please use a high output-bitrate such as 6000 or even a bit higher.


For recording sound, please activate your microphone in the mixer-tool of your Linux distribution and please select a recording volume which gives good use of the dynamic range of the A/D converter of your sound card. The GUI ( the small tuerquois rectangle ) also contains a reclevel meter. A good recording volume is achieved if the white bar in the reclevel meter is more than 2/3 full if sound is present. If the bar turns partly of fully red, this means that overdrive occurs which is an indication that the recording volume is too high.

Preview Playback

The GUI of the OpenGL/Animation-mode does not yet provide a preview playback button but you can use standard demorec for playback. For doing that please start demorec with the resolution of your video, e.g.,

demorec --width 1147 --height 833
Then load the video and press "play" for the preview playback.

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DemoRecorder Box
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        You explain something and ...
... everybody understands you.

Your wish is granted...
... with DemoRecorder.
DemoRecorder in the Media

A comparison of screencasting apps for Linux (including DemoRecorder)
(first published in Linux Format Magazine, issue July 2009.)

Interview on the Linux Link Tech Show. Please select Episode 154.

DemoRecorder featured in Linux-User Magazine (in German)

Your video can contain sound narration recorded from microphone.
View and listen to the example.
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