Answers.Body: <p>Just to add a little bit more info to SlimSCSI's straight up answer.</p>
  
  <blockquote>
    <p>Does youtube store different video files for different bit rate?</p>
  </blockquote>
  
  <p>Yes and no, for the 1080p stream YouTube utilizes a technique called <a href="http://en.wikipedia.org/wiki/Dynamic_Adaptive_Streaming_over_HTTP" rel="nofollow">DASH</a>. This serves essentially a video that was encoded with several different bitrates (though its one file) and adapts the bitrate on the fly according to bandwidth capabilities on the user side.</p>
  
  <p>This is not true for any other resolution lower than 1080p.</p>
  
  <blockquote>
    <p>Isn't that a disk space destroyer too?</p>
  </blockquote>
  
  <p>It does use up more disk space but disk space is very cheap nowadays.
  Destroyer? No, the increase in size is not that huge as the higher bitrate streams can "share" information with the lower bitrate ones.</p>
  
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2014-09-11T17:44:36.383Z
Answers.Text: Adapt bit rate on the fly ? Does it use special codec ? If it is the same codec, what happens internally in codec so that it encodes with different bit rate ? Is it something like bigger bitrate have max microblock that lower bitrate shares ?
Answers.UserDisplayName: cowboysaif
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2014-09-12T14:43:02.937Z
Answers.Text: Have a look at these articles:
  http://en.wikipedia.org/wiki/Adaptive_bitrate_streaming
  http://en.wikipedia.org/wiki/Scalable_Video_Coding
  http://www.hhi.fraunhofer.de/de/kompetenzfelder/image-processing/research-groups/image-video-coding/scalable-video-coding/svc-scalable-extension-of-h264avc.html
  
  The Frauenhofer one is very indepth.
Answers.UserDisplayName: timonsku
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2014-09-11T14:06:03.423Z
Answers.LastActivityDate: 2014-09-11T14:06:03.423Z
Answers.UserDisplayName: timonsku
Answers.Body: <blockquote>
    <p>Does youtube store different video files for different bit rate?</p>
  </blockquote>
  
  <ul>
  <li>Yes</li>
  </ul>
  
  <blockquote>
    <p>is the technique called "resampling" ?</p>
  </blockquote>
  
  <ul>
  <li>No</li>
  </ul>
  
  <blockquote>
    <p>Does youtube make live resampling for every user ?</p>
  </blockquote>
  
  <ul>
  <li>No</li>
  </ul>
  
  <blockquote>
    <p>All this things happens live ?</p>
  </blockquote>
  
  <ul>
  <li>No, not on youtube. But Yes on twitch.tv</li>
  </ul>
  
  <blockquote>
    <p>Or it encode and save different video files for different bitrate, so
    that when a user changes bitrate it servers that file.</p>
  </blockquote>
  
  <ul>
  <li>Yes</li>
  </ul>
  
  <blockquote>
    <p>Isn't that a disk space destroyer too ?</p>
  </blockquote>
  
  <ul>
  <li>Yes</li>
  </ul>
  
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2014-09-11T08:17:41.557Z
Answers.Text: Thanks ! Any idea why youtube does that ?
Answers.UserDisplayName: cowboysaif
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2014-09-11T16:24:05.797Z
Answers.Text: As opposed to transcoding everything on the fly? Because transcoding takes a ton of CPU resources. Better to do it just once.
Answers.UserDisplayName: SlimSCSI
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2014-09-11T01:58:32.907Z
Answers.LastActivityDate: 2014-09-11T02:39:09.860Z
Answers.LastEditDate: 2014-09-11T02:39:09.860Z
Answers.UserDisplayName: SlimSCSI
Body: <p>First of all, is the technique called "resampling" ?</p>
  
  <p>Does youtube make live resampling for every user ? Isn't it too cpu costly ? So far what i know about codecs is that it has to go through many encoding steps ( compression, motion prediction etc etc ). All this things happens live ?</p>
  
  <p>Or it encode and save different video files for different bitrate, so that when a user changes bitrate it servers that file. </p>
  
  <p>Isn't that a disk space destroyer too ?</p>
  
Tags: <video><codec><streaming>
Title: Does youtube store different video files for different bit rate?
UserDisplayName: cowboysaif
ThreadText: # Does youtube store different video files for different bit rate?
  
  (Asked by: username_0 on 2014-09-10)
  
  First of all, is the technique called "resampling" ?
  
  Does youtube make live resampling for every user ? Isn't it too cpu costly ? So far what i know about codecs is that it has to go through many encoding steps ( compression, motion prediction etc etc ). All this things happens live ?
  
  Or it encode and save different video files for different bitrate, so that when a user changes bitrate it servers that file.
  
  Isn't that a disk space destroyer too ?
  
  **Tags:** video, codec, streaming
  
  
  ---
  
  ## 2 answers
  
  ### Answer by username_2 on 2014-09-11. Score: 3 | Accepted answer
  
  > Does youtube store different video files for different bit rate?
  
  * Yes
  
  > is the technique called "resampling" ?
  
  * No
  
  > Does youtube make live resampling for every user ?
  
  * No
  
  > All this things happens live ?
  
  * No, not on youtube. But Yes on twitch.tv
  
  > Or it encode and save different video files for different bitrate, so
  > that when a user changes bitrate it servers that file.
  
  * Yes
  
  > Isn't that a disk space destroyer too ?
  
  * Yes
  
  > **Comments:**
  > **username_0**: Thanks ! Any idea why youtube does that ?  
  > **username_2**: As opposed to transcoding everything on the fly? Because transcoding takes a ton of CPU resources. Better to do it just once.  
  
  ---
  
  ### Answer by username_1 on 2014-09-11. Score: 1
  
  Just to add a little bit more info to username_2's straight up answer.
  
  > Does youtube store different video files for different bit rate?
  
  Yes and no, for the 1080p stream YouTube utilizes a technique called [DASH](http://en.wikipedia.org/wiki/Dynamic_Adaptive_Streaming_over_HTTP). This serves essentially a video that was encoded with several different bitrates (though its one file) and adapts the bitrate on the fly according to bandwidth capabilities on the user side.
  
  This is not true for any other resolution lower than 1080p.
  
  > Isn't that a disk space destroyer too?
  
  It does use up more disk space but disk space is very cheap nowadays.
  Destroyer? No, the increase in size is not that huge as the higher bitrate streams can "share" information with the lower bitrate ones.
  
  > **Comments:**
  > **username_0**: Adapt bit rate on the fly ? Does it use special codec ? If it is the same codec, what happens internally in codec so that it encodes with different bit rate ? Is it something like bigger bitrate have max microblock that lower bitrate shares ?  
  > **username_1**: Have a look at these articles: http://en.wikipedia.org/wiki/Adaptive_bitrate_streaming http://en.wikipedia.org/wiki/Scalable_Video_Coding http://www.hhi.fraunhofer.de/de/kompetenzfelder/image-processing/research-groups/image-video-coding/scalable-video-coding/svc-scalable-extension-of-h264avc.html  The Frauenhofer one is very indepth.  
  
  ---
  
  