No. When displaying a Media RSS feed, a BrightAuthor:connected presentation will play files as they are downloaded. The presentation waits up to five seconds per image. If an image file takes longer than five seconds to download, the unit skips to the next image in the feed. If a video file hasn't finished downloading, the unit skips to the next file until all feed items have been attempted.
The player will play feed items that are already downloaded while waiting for the rest of the feed to be completed.