NextStage can also capture RGBA footage as a .avi file, using either the Lagarith codec, or the CineForm codec.
Setting up the Codecs
NextStage does not include these codecs and accesses them through the VFW filter. They will have to be installed on your computer separately.
Once installed select your preferred codec in the Settings window, and press the "Codec" settings button.
Once open match these settings for Lagarith:
and these for CineForm:
You can adjust the amount of compression and file size by changing the "Encoding Quality" setting.