How to create a MPD file of MPEG-DASH to play a webm video?

问题:

I'm following this demo which uses mediaSource API and MPEG DASH standard to play a .webm video. This is the MPD file used:

<?xml version="1.0" encoding="UTF-8"?> <MPD   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"   xmlns="urn:mpeg:DASH:schema:MPD:2011"   xsi:schemaLocation="urn:mpeg:DASH:schema:MPD:2011"   type="static"   mediaPresentationDuration="PT888.05S"   minBufferTime="PT1S"   profiles="urn:webm:dash:profile:webm-on-demand:2012">   <Period id="0" start="PT0S" duration="PT888.05S" >   <AdaptationSet id="0" mimeType="video/webm" codecs="vp8" lang="eng" width="720"      height="306" subsegmentAlignment="true" subsegmentStartsWithSAP="1" bitstreamSwitching="true">   <Representation id="1" bandwidth="534144">     <BaseURL>mevq_logo_720x306_0250k_int-150-150.webm</BaseURL>     <SegmentBase indexRange="29052226-29054708">       <Initialization range="0-229" />     </SegmentBase>   </Representation>   <Representation id="2" bandwidth="1078766">     <BaseURL>mevq_logo_720x306_0500k_int-150-150.webm</BaseURL>     <SegmentBase indexRange="56003676-56006200">       <Initialization range="0-229" />     </SegmentBase>   </Representation>   <Representation id="3" bandwidth="1745140">     <BaseURL>mevq_logo_720x306_0750k_int-150-150.webm</BaseURL>     <SegmentBase indexRange="83686040-83688577">       <Initialization range="0-229" />     </SegmentBase>   </Representation>   <Representation id="4" bandwidth="2295403">     <BaseURL>mevq_logo_720x306_1000k_int-150-150.webm</BaseURL>     <SegmentBase indexRange="111588024-111590567">       <Initialization range="0-229" />     </SegmentBase>   </Representation>   <Representation id="5" bandwidth="3797938">     <BaseURL>mevq_logo_720x306_1500k_int-150-150.webm</BaseURL>     <SegmentBase indexRange="166960740-166963291">       <Initialization range="0-229" />     </SegmentBase>   </Representation>   <Representation id="6" bandwidth="6418657">     <BaseURL>mevq_logo_720x306_2000k_int-150-150.webm</BaseURL>     <SegmentBase indexRange="222165200-222167753">       <Initialization range="0-229" />     </SegmentBase>   </Representation> </AdaptationSet> <AdaptationSet id="1" mimeType="audio/webm" codecs="vorbis" lang="eng" audioSamplingRate="41000" subsegmentStartsWithSAP="1">   <Representation id="7" bandwidth="115479">     <BaseURL>evq_vorbis_128kbps_cues-5sec_tracks-2.webm</BaseURL>     <SegmentBase indexRange="11944509-11947524">       <Initialization range="0-4501" />     </SegmentBase>   </Representation> </AdaptationSet>

Does anybody know how to obtain/calculate the numbers 'SegmentBase indexRange' and 'Initialization range' for any video?

回答1:

indexRange contains Segment Index Box (sidx). It is basically metadata fragment that contains information about the fragments the player should request when downloading the file. This is a quote from the spec:

"indexRange specifies the byte range that contains the Segment Index in all Media Segments of the Representation. The byte range shall be expressed and formatted as a byte-range-spec as defined in RFC 2616, Clause 14.35.1. It is restricted to a single expression identifying a contiguous range of bytes."

sidx box is described in HERE and a parser can be found HERE and HERE(from dash.js project)

Initialization - According to spec:

"specifies the URL including a possible byte range for the Initialization Segment."

Hope it helped!

转载请标明出处:How to create a MPD file of MPEG-DASH to play a webm video?

文章来源: How to create a MPD file of MPEG-DASH to play a webm video?