No, when playing an Media RSS feed, a BrightAuthor presentation will play files as they are downloaded. The presentation will wait up to 5 seconds per image. If an image file takes longer than 5 seconds to download, the unit skips to the next image in the feed. If a video file has not finished downloading, the unit will skip 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.
It seems that 4.6 has broken with this.