If you want to import a video in your activity to present to your participants, you can do so without even going into the activity itself. In the activity details, go to the Documents and surveys and click “Manage content”.
Then click on Import from my computer. Select your video file.

The following formats are allowed on the Via platform: FLV, AVI, MPG, MPEG, MOV, WMV, MP4

(Note that the video size must not exceed 100 MB).