title: How to determine duration from mp4 init segment
body: <p>So here I have an init segment:
  <a href="http://people.mozilla.org/~jyavenard/mediatest/fragmented/facebook-paper_dash.mp4" rel="nofollow">http://people.mozilla.org/~jyavenard/mediatest/fragmented/facebook-paper_dash.mp4</a></p>
  
  <p>Now, all movie headers (mvhd atom), media header (mdhd) or track headers (tkhd atoms) indicate that the duration is 0.</p>
  
  <p>(can check with this page: <a href="http://people.mozilla.org/~jyavenard/tests/mse_mp4/paper-init.html" rel="nofollow">http://people.mozilla.org/~jyavenard/tests/mse_mp4/paper-init.html</a>)</p>
  
  <p>Yet, IE11 and Chrome reads the duration as 120.187s which makes sense as the original mp4 I extracted it from was 2 minutes long.</p>
  
  <p>Here is the details of this mp4 init segment:</p>
  
  <pre><code>    [ftyp] size=8+28
        major_brand = isom
        minor_version = 200
        compatible_brand = isom
        compatible_brand = iso2
        compatible_brand = avc1
        compatible_brand = mp41
        compatible_brand = dash
      [free] size=8+47
      [moov] size=8+1168
        [mvhd] size=12+96
          timescale = 1000
          duration = 0
          duration(ms) = 0
        [mvex] size=8+64
          [trex] size=12+20
            track id = 1
            default sample description index = 1
            default sample duration = 1001
            default sample size = 0
            default sample flags = 10000
          [trex] size=12+20
            track id = 2
            default sample description index = 1
            default sample duration = 1024
            default sample size = 0
            default sample flags = 0
        [trak] size=8+467
          [tkhd] size=12+80, flags=f
            enabled = 1
            id = 1
            duration = 0
            width = 1920.000000
            height = 1080.000000
          [mdia] size=8+367
            [mdhd] size=12+20
              timescale = 30000
              duration = 0
              duration(ms) = 0
              language = eng
            [hdlr] size=12+33
              handler_type = vide
              handler_name = VideoHandler
            [minf] size=8+282
              [vmhd] size=12+8, flags=1
                graphics_mode = 0
                op_color = 0000,0000,0000
              [dinf] size=8+28
                [dref] size=12+16
                  [url ] size=12+0, flags=1
                    location = [local to file]
              [stbl] size=8+218
                [stsd] size=12+138
                  entry-count = 1
                  [avc1] size=8+126
                    data_reference_index = 1
                    width = 1920
                    height = 1080
                    compressor = 
                    [avcC] size=8+40
                      Configuration Version = 1
                      Profile = Main
                      Profile Compatibility = 40
                      Level = 31
                      NALU Length Size = 4
                      Sequence Parameter = [67 4d 40 1f ec c0 3c 01 13 f2 e0 22 00 00 07 d2 00 01 d4 c0 1e 30 63 34]
                      Picture Parameter = [68 e9 78 f2 c8]
                [stts] size=12+4
                  entry_count = 0
                [stsc] size=12+4
                  entry_count = 0
                [stsz] size=12+8
                  sample_size = 0
                  sample_count = 0
                [stco] size=12+4
                  entry_count = 0
        [trak] size=8+407
          [tkhd] size=12+80, flags=f
            enabled = 1
            id = 2
            duration = 0
            width = 0.000000
            height = 0.000000
          [mdia] size=8+307
            [mdhd] size=12+20
              timescale = 48000
              duration = 0
              duration(ms) = 0
              language = eng
            [hdlr] size=12+33
              handler_type = soun
              handler_name = SoundHandler
            [minf] size=8+222
              [smhd] size=12+4
                balance = 0
              [dinf] size=8+28
                [dref] size=12+16
                  [url ] size=12+0, flags=1
                    location = [local to file]
              [stbl] size=8+162
                [stsd] size=12+82
                  entry-count = 1
                  [mp4a] size=8+70
                    data_reference_index = 1
                    channel_count = 2
                    sample_size = 16
                    sample_rate = 48000
                    [esds] size=12+30
                      [ESDescriptor] size=2+28
                        es_id = 2
                        stream_priority = 0
                        [DecoderConfig] size=2+20
                          stream_type = 5
                          object_type = 64
                          up_stream = 0
                          buffer_size = 0
                          max_bitrate = 192082
                          avg_bitrate = 192082
                          DecoderSpecificInfo = 11 90 56 e5 00 
                        [Descriptor:06] size=2+1
                [stts] size=12+4
                  entry_count = 0
                [stsc] size=12+4
                  entry_count = 0
                [stsz] size=12+8
                  sample_size = 0
                  sample_count = 0
                [stco] size=12+4
                  entry_count = 0
        [udta] size=8+90
          [meta] size=12+78
            [hdlr] size=12+21
              handler_type = mdir
              handler_name = 
            [ilst] size=8+37
              [.too] size=8+29
                [data] size=8+21
                  type = 1
                  lang = 0
                  value = Lavf55.12.100
  </code></pre>
  
  <p>I can't for the life of me figure out where it's getting that 120.187s duration...</p>
  
  <p>Any ideas?
  thanks</p>