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Progressive download describes the download process of digital media files, which allows a user to access a file's contents before the download has been completed. The end user's experience is very similar to that provided by streaming media, and the fact that the full file has not been downloaded is often unnoticeable. For slower connections, progressive download is often the preferred method because it allows playback directly from the user’s media player, thereby eliminating dependence on bandwidth.
Progressive downloading transmits a media file with metadata in the header of the downloaded file. A media player capable of progressive downloading reads this metadata and begins playback of the media file after a specified minimum portion of the data has been downloaded. Media players also require a buffer to hold data for use at a later time. The amount of data held in the buffer before playback is determined by both the producer of the content (in encoder settings) and by additional settings imposed by the media player. Prior to the development of progressive download, the referenced metadata was located at the end of the file. As such, no playback was possible before the entire file was downloaded.
The first file type capable of progressive download was the “.jpeg” image file. Apple was one of the first companies to use progressive download commercially, when it employed the technology in its QuickTime media player in 1997.
With streaming media, playback may stutter, or even stop, if it exceeds the file download rate. If data is downloaded from a Web page, it is temporarily stored in a folder associated with the Web browser; otherwise, the data is stored in a storage directory determined by the preferences settings of the media player used for playback. During a streaming media session, the file is never completely downloaded to a local storage device as it is with progressive download. This difference makes streaming media a more secure option that reduces the risk of piracy.
Progressive download is often a media player marketing feature.