MPD 파일에서 segment의 개수 구하기 (How to get the number of segment)

number of secment = second(mediaPresentationDuration) / (duration / timescale)

 

예를들어 아래의 파일에서 segment의 개수를 구한다고 가정해보자.

 

<?xml version="1.0" encoding="utf-8"?>
<MPD xmlns="urn:mpeg:dash:schema:mpd:2011" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="urn:mpeg:DASH:schema:MPD:2011 DASH-MPD.xsd" type="static" profiles="urn:mpeg:dash:profile:isoff-on-demand:2011" minBufferTime="PT2S" mediaPresentationDuration="PT6M36.554S">
  <Period id="0" start="PT0.0S">
    <AdaptationSet id="0" contentType="video" segmentAlignment="true" bitstreamSwitching="true">
      <Representation id="v_t0_MAIN" mimeType="video/mp4" codecs="avc1.4d401f" bandwidth="993082" width="854" height="480">
        <SegmentTemplate timescale="15360" presentationTimeOffset="0" duration="61440" initialization="v_t0_MAIN/init.m4s" media="v_t0_MAIN/$Number%06d$.m4s" startNumber="0"></SegmentTemplate>
      </Representation>
      <Representation id="v_t0_BASE" mimeType="video/mp4" codecs="avc1.4d401e" bandwidth="495528" width="640" height="360">
        <SegmentTemplate timescale="15360" presentationTimeOffset="0" duration="61440" initialization="v_t0_BASE/init.m4s" media="v_t0_BASE/$Number%06d$.m4s" startNumber="0"></SegmentTemplate>
      </Representation>
      <Representation id="v_t0_HIGH" mimeType="video/mp4" codecs="avc1.64001f" bandwidth="1993939" width="1280" height="720">
        <SegmentTemplate timescale="15360" presentationTimeOffset="0" duration="61440" initialization="v_t0_HIGH/init.m4s" media="v_t0_HIGH/$Number%06d$.m4s" startNumber="0"></SegmentTemplate>
      </Representation>
      <Representation id="v_t0_HIGH4" mimeType="video/mp4" codecs="avc1.640028" bandwidth="6004008" width="1920" height="1080">
        <SegmentTemplate timescale="15360" presentationTimeOffset="0" duration="61440" initialization="v_t0_HIGH4/init.m4s" media="v_t0_HIGH4/$Number%06d$.m4s" startNumber="0"></SegmentTemplate>
      </Representation>
      <Representation id="v_t0_LOW" mimeType="video/mp4" codecs="avc1.4d4015" bandwidth="151863" width="426" height="240">
        <SegmentTemplate timescale="15360" presentationTimeOffset="0" duration="61440" initialization="v_t0_LOW/init.m4s" media="v_t0_LOW/$Number%06d$.m4s" startNumber="0"></SegmentTemplate>
      </Representation>
    </AdaptationSet>
    <AdaptationSet id="1" contentType="audio" lang="ko" segmentAlignment="true" bitstreamSwitching="true">
      <Representation id="a_t0_128-44100" mimeType="audio/mp4" codecs="mp4a.40.2" bandwidth="130661" audioSamplingRate="44100">
        <AudioChannelConfiguration schemeIdUri="urn:mpeg:dash:23003:3:audio_channel_configuration:2011" value="2"></AudioChannelConfiguration>
        <SegmentTemplate timescale="44100" presentationTimeOffset="0" duration="176400" initialization="a_t0_128-44100/init.m4s" media="a_t0_128-44100/$Number%06d$.m4s" startNumber="0"></SegmentTemplate>
      </Representation>
      <Representation id="a_t0_320-44100" mimeType="audio/mp4" codecs="mp4a.40.2" bandwidth="322704" audioSamplingRate="44100">
        <AudioChannelConfiguration schemeIdUri="urn:mpeg:dash:23003:3:audio_channel_configuration:2011" value="2"></AudioChannelConfiguration>
        <SegmentTemplate timescale="44100" presentationTimeOffset="0" duration="176400" initialization="a_t0_320-44100/init.m4s" media="a_t0_320-44100/$Number%06d$.m4s" startNumber="0"></SegmentTemplate>
      </Representation>
      <Representation id="a_t0_96-44100" mimeType="audio/mp4" codecs="mp4a.40.2" bandwidth="98654" audioSamplingRate="44100">
        <AudioChannelConfiguration schemeIdUri="urn:mpeg:dash:23003:3:audio_channel_configuration:2011" value="2"></AudioChannelConfiguration>
        <SegmentTemplate timescale="44100" presentationTimeOffset="0" duration="176400" initialization="a_t0_96-44100/init.m4s" media="a_t0_96-44100/$Number%06d$.m4s" startNumber="0"></SegmentTemplate>
      </Representation>
    </AdaptationSet>
  </Period>
</MPD>

 mediaPresentationDuration="PT6M36.554S" 이므로 플레이타임을 초로 변환하면 6*60 + 36.554 = 396.554초 이다

video파일의 duration은 61440, timescale은 15360, audio의 duration은 176400, timescale은 44100이다. 

따라서 playtime per segment = 61440/15360, 176400/44100 이므로, 비디오와 오디오 파일 각각의 재생 길이는 4초임을 알 수 있다.

따라서 396.554 / 4 = 99.1385이므로 100개의 segment를 가지는 것을 알 수 있다.

위에서 start number의 값은 0으로 지정되어있으므로 동영상 재생에 필요한 segment를 불러올 때는 0~99까지 총 100개의 segment를 불러오는 것을 알 수 있다.