You can start watching a video as it's being downloaded.
When there's enough downloaded content for playback, the play button becomes activated and you can start watching the video.
If you've watched the video before, playback will resume seamlessly from where you left off. You can also jump to any part of the downloaded content and start to watch from there.
Note: HTC Watch only keeps track of the last playback position of your 16 most recently watched videos.