Menu
Home
People
Places
Arts
History
Plants & Animals
Science
Life & Culture
Technology
Reference.org
Progressive download
open-in-new
<h2 id="history">History</h2> <p>Initially the digital media file type known as <a href="/facts/JPEG/HQ8QS3uB">JPEG</a> was the first visual media to render a progressive visual display as the digital media was downloaded and actually referred to as a progressive download. The distinction between the technical behavior of progressive download as opposed to the common or commercial use of the term progressive <a href="/facts/Download/qN7fWmyI">download</a> 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. <a href="/facts/Apple_computer/oTJYta3k">Apple</a> in reference to their <a href="/facts/QuickTime/rA3GQp2j">QuickTime</a> media player employed the term <i>Fast Start</i><a class="footnote-ref" id="fnref:1" href="#fn:1"><sup>1</sup></a> in 1997, to describe what was commercially referred to as progressive download playback of <a href="/facts/Encoding/CSntvnEo">encoded</a> <a href="/facts/Digital_media/QLXzDrhL">digital media</a> content. </p> <h2 id="http-progressive-download-versus-streaming-media">HTTP progressive download versus streaming media</h2> <p>The end user experience is similar to <a href="/facts/Streaming_media/4rPhSq0Y">streaming media</a>; however, the file is downloaded to a physical drive on the end user's device. It is typically stored in the <a href="/facts/Temporary_directory/8USmCS4N">temporary directory</a> of the associated web browser if the medium was embedded in a web page or is diverted to a storage directory that is set in the preferences of the media player used for playback. The file will stutter or stop playback if the rate of playback exceeds the rate at which the file is downloaded. The file will begin to play again after further download. </p><p>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. Prior to that change, the meta data summary was located at the end of a media file and the entire file would need to be downloaded in order for the meta data to be read and the player begin playback.<a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a> </p><p>HTTP Pseudo-streaming (or progressive download), similar to <a href="/facts/Streaming_media/4rPhSq0Y">streaming media</a> or <a href="/facts/HTTP_Live_Streaming/ryHrK3aF">HTTP Live Streaming</a>, also supports <a href="/facts/Adaptive_bitrate_streaming/K3oSzyJB">adaptive bitrate streaming</a>. The disadvantage of HTTP Pseudo-streaming over <a href="/facts/Streaming_media/4rPhSq0Y">streaming media</a> is reduced security, since HTTP is easier to <a href="/facts/Packet_analyzer/mFQP7gWB">sniff</a> compared to <a href="/facts/Real-Time_Messaging_Protocol/6rpAXGgk">RTMP</a>, along with long loading times when seeking larger videos.<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a> </p> <h2 id="optimization-for-http-pseudo-streaming">Optimization for HTTP Pseudo-streaming</h2> <p>The <a href="/facts/MPEG-4_Part_14/PM0FNvUU">MP4</a> files consist of <a href="/facts/Chunk_(information)/zj9m70KU">chunks of data</a>, called atoms. These atoms stores information like subtitles, etc. The special atom, called <i>moov atom</i> is responsible for storing information regarding how to play the video like <a href="/facts/Display_resolution/8LQTWvl3">dimensions</a>, <a href="/facts/Frame_rate/sbRkc9xa">frames per second</a> and such which is important to begin playing a video on <a href="/facts/HTML_video/DKUclA1k">HTML video</a> player.<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a> But atoms can appear in any order, so web servers like <a href="/facts/Nginx/AlTYUuTp">Nginx</a> spends some CPU, memory and disk I/O to find the <i>moov atom</i> so that <a href="/facts/HTML_video/DKUclA1k">HTML video</a> based clients can start playing the video. To optimize for HTTP Pseudo-streaming, it's important to move the <i>moov atom</i> to the beginning, so that web servers like <a href="/facts/Nginx/AlTYUuTp">Nginx</a> optimize for faster pseudo-streaming resulting in playing of playbacks without having to wait for the entire file to arrive or to be scanned.<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a> </p><p> ffmpeg -i sample_input.mp4 -movflags faststart -acodec copy -vcodec copy sample_output.mp4 </p> <ul><li> -movflags faststart does the optimization by moving the index (moov atom) to the beginning of the file.<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a></li> <li> -acodec copy extracts the audio from the input file unaltered.</li> <li> -vcodec copy extracts the video from the input file unaltered.</li></ul> <p>By doing this optimization, we effectively prevent web servers, like <a href="/facts/Nginx/AlTYUuTp">nginx</a>, from spending relative amount of computation in finding the moov atom hence increasing the playback performance on <a href="/facts/HTML_video/DKUclA1k">HTML video</a> based client.<a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a><a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a> </p> <h2 id="seeking">Seeking</h2> <p>Initially, the file is played from the beginning. A user may wish to point to a part of the file which haven't been downloaded yet. This capability is called seeking<a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a> and it makes possible to download and start playing any part of the media file. That is often referred to as pseudo-streaming. </p><p>For <a href="/facts/Flash_video/rbbPoE7H">Flash video</a> seeking requires a list of seek points in the media file metadata. These points are offsets in the video (both in seconds and bytes) at which a new key frame starts. A web server or a media server which handles the download, must support seek points in query string of requests for downloading data. </p><p>For other types of media files such as <a href="/facts/MP4/PM0FNvUU">MP4</a> or <a href="/facts/Matroska/hDrffBx0">MKV</a>, web servers must be capable of handling a special offset parameter. The offset parameter name differs for various servers so it must be specified in player settings. </p><p>Some servers support seeking via additional modules only, they are specified below. Seeking parameter names are written in <i>italic</i>. </p> <table><tbody><tr><th>Server</th><th>Flash seeking</th><th>MP4 seeking</th></tr><tr><td><a href="/facts/Apache_HTTP_Server/tcmWYYUq">Apache HTTP Server</a></td><td><a href="http://h264.code-shop.com/trac">mod_h264</a> <i>start</i> <a href="https://github.com/osantana/mod_flvx">mod_flvx</a> <i>start</i></td><td><a href="http://h264.code-shop.com/trac">mod_h264</a> <i>starttime</i></td></tr><tr><td><a href="/facts/Lighttpd/NTJLA4H6">lighttpd</a></td><td><i>start</i></td><td><a href="http://h264.code-shop.com/trac">mod_h264</a> <i>starttime</i></td></tr><tr><td><a href="/facts/Nginx/AlTYUuTp">Nginx</a></td><td><a href="http://nginx.org/en/docs/http/ngx_http_flv_module.html">http_flv_module</a> <i>start</i></td><td><a href="http://nginx.org/en/docs/http/ngx_http_mp4_module.html">http_mp4_module</a> <i>start</i></td></tr><tr><td><a href="/facts/Nimble_Streamer/F6Qpetb8">Nimble Streamer</a></td><td><i>start</i></td><td><i>start</i></td></tr></tbody></table> <h2 id="see-also">See also</h2> <ul><li><a href="/facts/Online_video_platform/tNBgCRKy">Online video platform</a></li> <li><a href="/facts/Video_streaming/4rPhSq0Y">Video streaming</a></li></ul> <h2 id="external-links">External links</h2> <ul><li><a href="https://web.archive.org/web/20100818043044/http://dowire.org/wiki/Streaming_vs_Progressive_Download"><i>Streaming vs Progressive Download</i></a>, archived from <a href="http://dowire.org/wiki/Streaming_vs_Progressive_Download">the original</a> on 2010-08-18</li> <li><a href="http://www.microsoft.com/windows/windowsmedia/compare/webservvstreamserv.aspx"><i>Web Server vs. Streaming Server</i></a>, Microsoft, retrieved 2010-09-21</li> <li><a href="http://www.mediacollege.com/adobe/flash/streaming/progressive-download.html"><i>Flash Video: Progressive Download</i></a>, retrieved 2010-09-21</li> <li><a href="https://web.archive.org/web/20150529160756/http://witalks.com/video-streaming-vs-progressive-downloading-or-http-streaming/"><i>Video Streaming Vs Progressive Download</i></a>, archived from <a href="http://witalks.com/video-streaming-vs-progressive-downloading-or-http-streaming/">the original</a> on 2015-05-29, retrieved 2015-05-29</li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>QuickTime Streaming Server 4.1 (PDF), archived from the original (PDF) on 2011-07-06, retrieved 2010-09-21, Two methods are commonly used to deliver media over the web for real-time viewing: progressive download (Fast Start) and real-time streaming. <a href="https://web.archive.org/web/20110706224514/http://sysdoc.doors.ch/APPLE/L29080A_QTSS41_DS.pdf" target="_blank">https://web.archive.org/web/20110706224514/http://sysdoc.doors.ch/APPLE/L29080A_QTSS41_DS.pdf</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>Understanding the MPEG-4 movie atom, retrieved 2015-07-17 <a href="http://www.adobe.com/devnet/video/articles/mp4_movie_atom.html" target="_blank">http://www.adobe.com/devnet/video/articles/mp4_movie_atom.html</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>Peter Luk. "Video Delivery: HTTP Pseudo-Streaming". <a href="https://staff.ie.cuhk.edu.hk/~sfluk/wordpress/?p=2590" target="_blank">https://staff.ie.cuhk.edu.hk/~sfluk/wordpress/?p=2590</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>Billy Hoffman (2016). "Optimizing MP4 Video for faster streaming". <a href="https://rigor.com/blog/optimizing-mp4-video-for-fast-streaming/" target="_blank">https://rigor.com/blog/optimizing-mp4-video-for-fast-streaming/</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>"Module ngx_http_mp4_module". <a href="https://nginx.org/en/docs/http/ngx_http_mp4_module.html" target="_blank">https://nginx.org/en/docs/http/ngx_http_mp4_module.html</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>"FFmpeg Formats Documentation". <a href="https://ffmpeg.org/ffmpeg-formats.html" target="_blank">https://ffmpeg.org/ffmpeg-formats.html</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>"Module ngx_http_mp4_module". <a href="https://nginx.org/en/docs/http/ngx_http_mp4_module.html" target="_blank">https://nginx.org/en/docs/http/ngx_http_mp4_module.html</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> <li id="fn:8"><p>Billy Hoffman (2016). "Optimizing MP4 Video for faster streaming". <a href="https://rigor.com/blog/optimizing-mp4-video-for-fast-streaming/" target="_blank">https://rigor.com/blog/optimizing-mp4-video-for-fast-streaming/</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li> <li id="fn:9"><p>Pseudo Streaming in Flash, retrieved 2015-07-17 <a href="http://support.jwplayer.com/customer/portal/articles/1430518-pseudo-streaming-in-flash" target="_blank">http://support.jwplayer.com/customer/portal/articles/1430518-pseudo-streaming-in-flash</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li> </ol>