Currently the video upload feature is only available via the app (i.e. not via the web). To upload a video using the app:
In the group album you want to add a video to select the icon to add content (Android: the icon in the top right-hand corner of the screen of a photo with a plus sign; iPhone/iPad: the blue button with the plus sign in the middle of the task bar at the bottom of the screen.) Then select the "Video" option when it asks you what you would like to share.
Video uploads have a time limit of 15 seconds, which you will be asked to trim after uploading (if the file you selected is too long).
At this point we do not support animated .gif files.