If you get a warning message when inserting an MP4 video that says "Unsupported Codec", the video will not play correctly in the published output.
The Flash Player only supports playback of MP4 videos encoded with the H.264 codec.
To correct this issue, do either of the following:
Encode the MP4 to FLV using Articulate Video Encoder '09.
Or, re-encode the MP4 movie using the H.264 codec.