Kathy answered that it doesn't, but she has noticed recently that the final pass to complete the image isn't always made. They are not supported on all browsers, but they do a better jobs than gifs for photos. Use LD Pro on a PC or Transparency on a Mac to make a color transparent. Transparency will take one color in the graphic, typically the background color, and make it transparent so that the browser's background shows through. Although audio can be done in .wav, .aaif, and .au files, it is best to use .au files because most users have the helper app configured to play that file type.
Audio files are often big and take a lot of time to download.
Only use video when nothing else will do. The file size will vary considerably between the two. You can use Sparkle to create a video. And we briefly discussed the idea of having a video camera pointed at the old well. Jason Purdy volunteered to check into what would be required to do this.