How can I play .camrec files made in Camtasia?

You can use 7-Zip to open .camrec files, it's possible it's just a renamed extension. The video is .AVI inside, however, if you've recorded system audio, it stores it as a separate WAV file, and the Microphone or other selected audio source is encoded into the AVI. I had a great batch process to unpack, remux (to overwrite the microphone with system audio) and encode camrecs to AVI with commandline 7-Zip and virtualdub, but unfortunately lost it in a hard drive crash a few months ago. Have to work on it again... in any case, just knowing 7-Zip can handle camrecs without having to open Camtasia Studio is valuable enough. I know there's a 7-Zip linux port; none for virtualdub but it shouldn't be too hard to find an alternative.

Since none of the current (as of Friday, 12th October, 2012) softwares support *.camrec, you might have to convert *.camrec to *.AVI before watching the videos in Ubuntu.

How to convert *.camrec to *.AVI:

1. Open "Camtasia Studio." Click "Import media." Select on the window the ".Camrec" file you wish to convert to ".AVI." Click "Open."
2. Drag the file, which has appeared in the clip bin, onto the time line at the bottom of the screen.
3. Click "Produce video as..." on the left-hand side of the window. Select "Custom production settings" and click "Next." Select "AVI video" from the list of formats. Click "Next" four times, which will take you through all of the video settings. Type a "Production name" into the box at the top and select a location for the file to be saved. Click "Finish." Once it is converted, the video will play and be saved to your selected location.

—How to Convert Camrec to AVI | eHow.com

If you don't have access to Camtasia Studio, you can also extract the recorded video from the CAMREC file.

Just rename the file, changing the CAMREC extension to ZIP. Open the new file with the ZIP extension with the free 7-Zip program. You'll find several files inside, including Screen_Stream.avi - this is the actual screen recording file in AVI format. Extract that file.