Progressive download

A progressive download is the transfer of digital media files from a server to a client, typically using the HTTP protocol when initiated from a computer.

The distinction between the technical behavior of progressive download as opposed to the common or commercial use of the term progressive download to describe that behavior was not documented and there is a good deal of question regarding the origin of the term versus the origin of the technical implementation.

The end user experience is similar to streaming media, however the file is downloaded to a physical drive on the end user's device; the file is typically stored in the temporary directory of the associated web browser if the medium was embedded into a web page or is diverted to a storage directory that is set in the preferences of the media player used for playback.

This fast start playback is the result of moving the meta data from the end of the digital media file to the front, this move of the meta data gave the media player all the information it required to begin playback as the file was still being downloaded.

By doing this optimization, we effectively prevent web servers, like nginx, from spending relative amount of computation in finding the moov atom hence increasing the playback performance on HTML video based client.

This capability is called seeking[7] and it makes possible to download and start playing any part of the media file.

For other types of media files such as MP4 or MKV, web servers must be capable of handling a special offset parameter.