Progressive Download

A Progressive Download ( German: Progressive Download ) is the transfer of digital media files from a server to a client. Typically, the HTTP protocol is used when transferring from one computer is initiated. The user can already start playback before the media file has been fully downloaded. The crucial difference between streaming and progressive download of media files is as the digital media file is received and stored by the end user's device.

A media player that is capable of progressive download playback is dependent on intact metadata in the header of the file, as well as to a local buffer of the digital media file that was downloaded from the web server. From the time at which a certain amount of data is available at the local reproducing apparatus, the medium is played back. The specific size of this buffer has been embedded by the manufacturer of the file content in the encoder settings of the file. It is supplemented by additional buffer settings of the media player.

History

Originally, the digital media file type JPEG was the first visual medium to build a progressive image display, even during the digital medium has been downloaded, and was therefore referred to as a progressive download. The distinction between the technical behavior of Progressive Download in contrast to the usual use of the term progressive download to describe this behavior has not been documented, and there are many questions concerning the origin of the term in comparison to the technical implementation. In 1997, Apple used in the reference of its QuickTime media player the concept of fast start to describe what is commonly referred to as progressive download playback of encoded digital media content.

The rapid onset of the performance was the result of a shift of the metadata from the end of the digital media file to its beginning. This shift of the metadata gave the media player all the information he needed to start playing, even while the file was downloaded. Before this change, the metadata were stored at the end of the digital media file and the whole file had to be downloaded to read the metadata and to let the media player begin playback.

Progressive download compared to Streaming Media

The perception of the end user is similar to that in streaming media. If a digital media file is embedded in a web page, it will be downloaded into the memory of the device by the end user. The digital media file is typically stored either in the temporary directory of the web browser involved or redirected to a directory that is specify in the settings of the Media Player for playback. Playback of digital media file will stutter or even stop when the data rate for playback exceeds the data rate for the download. If again enough data has been downloaded, the file will be played.

First, a media file is played as fast as possible from its very inception. The user can now have the desire to jump to a time of reproduction, which has not even been downloaded. This possibility is described coil and allows download any portion of the media file and fed back pass. This is also known as the pseudo - streaming.

When coils in Flash videos a list of Spulpunkten is needed in the metadata of the media file. These points are offset in the video ( specified both in bytes and in seconds ) in which a new section begins. A web server or a media server, edit the a download must support the requests for data to be downloaded such Spulpunkte.

For other types of media files like MP4 or MKV in the web server must be able to deal with special offset parameters. The names of the offset parameters differ for the various servers and must therefore be specified in the settings of the media player.

Some servers support the coils with additional modules, which are indicated in the table below. The names of the winding parameters are written in italics.

Mod_h264 startTime