video streaming - What does segmentrange in a mpd file mean? -

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i got sample mpd file http://dash-mse-test.appspot.com/media.html , below snippet containing single representation.

   ...    <representation bandwidth="4190760" codecs="avc1.640028" height="1080" id="1" mimetype="video/mp4" width="1920">     <baseurl>car_cenc-20120827-89.mp4</baseurl>     <segmentbase indexrange="2755-3230">       <initialization range="0-2754" />     </segmentbase>   </representation>   ...

what segmentbase mean? value of indexrange mean?

initialization end range 1 less indexrange start value. ie., in above 2755-1 = 2754 (the value of initialization)

can me understand significance of these number?

edit 1:

as per answer @sander below, understand segmentindex byte range. however, still confused how use value.

for eg: <representation bandwidth="4190760" codecs="avc1.640028" height="1080" id="1" mimetype="video/mp4" width="1920"> <baseurl>car-20120827-89.mp4</baseurl> <segmentbase indexrange="674-1149"> <initialization range="0-673" /> </segmentbase> </representation>

there 1 segment in representation containing entire video clip in single file. (the file size 90mb).

initialization range mentions 0-673. 0th byte of file 673rd byte of file contains initialization segment video. understanding right?

if so, file 90mb. how 1 other segments byte range? segmentbase mentions indexrange 674-1149.

btw, using player understand segmentindex.

http://dash-mse-test.appspot.com/dash-player.html?url=http://yt-dash-mse-test.commondatastorage.googleapis.com/media/car-20120827-manifest.mpd

looking @ header request sent using chrome's inspect tool, there lot of request happening in small byte ranges not sure how 1 these byte ranges mpd.

thanks

the exact format of file described in dash specification (iso/iec 23009-1). segmentbase element described in chapter 5.3.9.2.

my interpretation of snippet representation consists of single mp4 file delivered player 1 segment. indexrange range of bytes within segment represents segment index (the sidx box in mp4 file) , initialization element indicates range of bytes includes relevant initialization data (the various header boxes in mp4 file). note, ranges neatly cover beginning of segment, rest presumably filled media sample data. byte ranges inform player should load relevant data from.

edit: sidx box contains byte ranges reference sub-segments of single mp4 file. quoting iso/iec 14496-12:2012(e):

each segment index box documents how (sub)segment divided 1 or more subsegments (which may further subdivided using segment index boxes).

a subsegment defined time interval of containing (sub)segment, , corresponds single range of bytes of containing (sub)segment. durations of subsegments sum duration of containing (sub)segment.

based on contents of sidx box, player can determine parts of mp4 file needs download in order play specific piece of video.


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