You can easily get around this by capturing your screen with QuickTime and converting the resulting video with ffmpeg via command line.
First fire up your android emulator, or desktop version of your Libgdx game.
Then start QuickTime Player. In the top menu go to File > New Screen Recording.
When you press the red record button, drag a rectangle to select a portion of the screen to record, and record your video. To stop recording, use the circle icon on the top right.
Save your video as video.mov on your desktop.
Now you need the conversion tool: ffmpeg. We'll install it using the terminal via Homebrew. If you are not familiar with it, homebrew is the famous 3rd party package manager for OSX, read about it here - http://brew.sh/
Open the terminal and use this command to install ffmpeg
brew install ffmpeg --with-libvpx
After installing, navigate to your desktop folder
and convert your video. The following command is for creating a h264 video for Twitter.
ffmpeg -i video.mov -r 30 -c:v libx264 -b:v 1M -vf scale=640:-1 video.mp4
Do you want to post your game progress to 4chan's /agdg/? The following command will create a webm with VP8 codec suitable for posting on 4chan.
ffmpeg -i video.mov -c:v libvpx -crf 10 -b:v 1M -vf scale=640:-1 video.webm
The video will be created in the same folder of your source video (your desktop). If you want to mess with ffmpeg parameters like scaling, bitrate, etc, refer to the ffmpeg wiki.