Whether using Web or Streaming delivery, the size of the movie that can be delivered depends upon the bandwidth available to the user. An ethernet connection can receive a much larger, higher quality movie than a dial-up modem.
Because of the user's bandwidth limitation, consider providing multiple versions of the movie. Allow the user to choose which movie instead of deciding for the user. Even though many of the popular formats allow for automatic detection of the user's connection speed, allow the user to make the choice as he or she may opt for a lower bandwidth version of the movie for a variety of reasons.
Although generally not an issue, the number of users connecting to the UMD server can impact available bandwidth. As with any resource, make wise use of what's available.