Reads the file and outputs it in chunks rather than all at once, reducing the amount of memory needed to very little, even for very very large files.
Supports http request ranges so that only parts of the file will be returned if requested. This allows in-browser video players to seek to arbitrary points in the video without needing to download the whole file.
Makes use of flush during send to allow the browser to being receiving file data immediately, allowing streamable video formats to begin playing before the server has finished sending the data. This could also be used in the future to add a transmission rate limiter.
Has early-disconnect detection, to terminate sending file data if the client browser has disconnected or aborted (for instance, a user starts a video, then seeks to near the middle, the first request of data will be terminated rather than continuing to process the file).