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• How to correctly calculate which segments are ready to be downloaded using MPEG-DASH

  24 avril 2019, par igal k

  What i’m trying to do ?

  Write a simple MPEG-DASH client using the SegmentTemplate pattern to calculate which segments are ready to be downloaded for a live source.

  A picture taken using chrome’s debugging tools at a moment X showing an mpd request(8af651fd747.....mpd) and the actual segments fetched respectfully to that request.

  

  Given the following MPD

  <mpd availabilitystarttime="2019-04-24T06:43:32Z" maxsegmentduration="PT4.096S" minbuffertime="PT4.096S" minimumupdateperiod="PT15.835S" profiles="urn:mpeg:dash:profile:isoff-live:2011" publishtime="2019-04-24T11:14:01Z" suggestedpresentationdelay="PT11.878S" timeshiftbufferdepth="PT65.536S" type="dynamic" xmlns="urn:mpeg:dash:schema:mpd:2011">
  
    <location>https://content-aaps1.uplynk.com/channel/8af651fd7473474f86a05ffb0a1c8972.mpd?rmt=wv&amp;amp;cid=8af651fd7473474f86a05ffb0a1c8972&amp;amp;oid=600e5c27541344a1bf3818617ad712ce&amp;amp;prettydash=1&amp;amp;exp=1556091088&amp;amp;rn=4138683939&amp;amp;tc=1&amp;amp;ct=c&amp;amp;sig=5fb7f0c18f3f1d2ad4fdee53c02c1e1ed904bc5e8474f4ebf886d209ff7f21c9&amp;amp;pbs=05b6594bcf4b4728ac1094976a80194d</location>
  
    <period start="PT2826.240S">
  
      <adaptationset maxframerate="30" maxheight="720" maxwidth="1280" mimetype="video/mp4" segmentalignment="true" startwithsap="1">
  
        <representation bandwidth="2604473" codecs="avc1.64001e" framerate="30" height="360" scantype="progressive" width="640">
  
          <baseurl>https://x-default-stgec.uplynk.com/aapm/slices/8c1/600e5c27541344a1bf3818617ad712ce/8c1027496a964b049f1bd5895f8f0412/</baseurl>
  
          <segmenttemplate duration="368640" initialization="https://x-default-stgec.uplynk.com/aapm/slices/8c1/600e5c27541344a1bf3818617ad712ce/8c1027496a964b049f1bd5895f8f0412/$RepresentationID$_init.mp4?pbs=05b6594bcf4b4728ac1094976a80194d&amp;amp;_jt=l&amp;amp;chid=8af651fd7473474f86a05ffb0a1c8972" media="$RepresentationID$$Number%08d$.m4f?pbs=05b6594bcf4b4728ac1094976a80194d&amp;amp;_jt=l&amp;amp;chid=8af651fd7473474f86a05ffb0a1c8972" presentationtimeoffset="254361599" startnumber="690" timescale="90000"></segmenttemplate>
  
        </representation>
  
      </adaptationset>
  
    </period>
  
    <utctiming schemeiduri="urn:mpeg:dash:utc:http-iso:2014" value="https://content-aaps1.uplynk.com/misc/utcservertime"></utctiming>
  
  </mpd>

  I see that the next segment request should be #3955

  What i have tried so far

      period.end = 1556104456;
  
      period.start = 2826;
  
      availability_start_time = 1556088212;
  
      max_segment_duration = 4;
  
      time_shift_buffer_depth = 65

  So, first of all, i read DASH-IF-IOP 4.3 section 4.3.4.2 page #82 and implemented the following code :

     int k1 = 1;
  
  int period_duration = period.end - (period.start + data_.availability_start_time);
  
  int k2 = ceil((float)period_duration / (float)data_.max_segment_duration);
  
  double duration = ((float)representation.duration / (float)representation.timeScale);
  
  size_t live_edge = std::min(
  
      (int)floor((float)((data_.publish_time - data_.availability_start_time - period.start) / duration)), k2);
  
  
  
  size_t oldest = std::max(k1, (int)floor((float)((data_.publish_time - data_.availability_start_time - period.start -
  
                                                      data_.time_shift_buffer_depth) /
  
                                                  duration)));

  after calculating everything : k1=1, k2=3355, live_edge=3272 and oldest=3256

  Also tried using ffmpeg’s dashdec.c

  for min_segment :

  if (c->is_live && pls->fragment_duration)
  
      {
  
          num = pls->first_seq_no + (((get_current_time_in_sec() - c->availability_start_time) - c->time_shift_buffer_depth) * pls->fragment_timescale) / pls->fragment_duration;
  
      }

  for max_segment :

  num = pls->first_seq_no + (((get_current_time_in_sec() - c->availability_start_time)) * pls->fragment_timescale) / pls->fragment_duration;

  after a small modification :

  size_t pmax = (((data_.publish_time - data_.availability_start_time))) / duration;
  
  size_t pmin = ((data_.publish_time - data_.availability_start_time) - data_.time_shift_buffer_depth) / duration;

  pmin=3946 pmax=3961

  in the ffmpeg example, i had to manually remove the first_seq_no variable because it looked like i doubled added the SegmentTemplate@StartNumber.

  even after succeeding in this task, how do i exactly build the request list of Segment(NOW) ----> Segment(LIVE_EDGE)

• Shaka Player : ignore empty AdaptationSet

  24 juin 2019, par Mitya

  I’m trying to play DASH stream in Shaka Player.
  Sometimes the stream doesn’t have an audio source and its manifest file contains an empty AdaptationSet entry.
  In this case Shaka Player returns the manifest parsing error :

  | DASH_EMPTY_ADAPTATION_SET | 4003 | number |  The DASH Manifest contained an AdaptationSet with no Representations. |

  Is it possible to ignore this error somehow and play the video without audio source ?

  Example of manifest file :

  <?xml version="1.0" encoding="utf-8"?>
  
  <mpd xmlns="urn:mpeg:dash:schema:mpd:2011" profiles="urn:mpeg:dash:profile:isoff-live:2011" type="dynamic" minimumupdateperiod="PT4S" suggestedpresentationdelay="PT4S" availabilitystarttime="2019-06-24T13:38:04Z" publishtime="2019-06-24T13:38:34Z" timeshiftbufferdepth="PT14.9S" minbuffertime="PT9.9S">
  
      <programinformation>
  
          
  
      </programinformation>
  
      <period start="PT0.0S">
  
          <adaptationset contenttype="video" segmentalignment="true" bitstreamswitching="true">
  
              <representation mimetype="video/mp4" codecs="avc1.640028" bandwidth="2000000" width="1920" height="1080" framerate="20/1">
  
                  <segmenttemplate timescale="10240" initialization="init-stream$RepresentationID$.m4s" media="chunk-stream$RepresentationID$-$Number%05d$.m4s" startnumber="5">
  
                      <segmenttimeline>
  
                          <s t="201697" d="51190" r="2"></s>
  
                      </segmenttimeline>
  
                  </segmenttemplate>
  
              </representation>
  
          </adaptationset>
  
          <adaptationset contenttype="audio" segmentalignment="true" bitstreamswitching="true">
  
          </adaptationset>
  
      </period>
  
  </mpd>

• Problems piping ffmpeg to flac encoder

  19 mai 2019, par Sebastian Olsen

  I need to encode a flac file with seektables, ffmpeg’s flac encoder does not include seektables, so I need to use the flac CLI. I’m trying to make it possible to convert any arbitrary audio file to a seekable flac file by first piping it through ffmpeg, then to the flac encoder.

  export const transcodeToFlac: AudioTranscoder<{}> = ({
  
    source,
  
    destination
  
  }) => {
  
    return new Promise((resolve, reject) => {
  
      let totalSize = 0
  
  
  
      const { stdout: ffmpegOutput, stderr: ffmpegError } = spawn("ffmpeg", [
  
        "-i",
  
        source,
  
        "-f",
  
        "wav",
  
        "pipe:1"
  
      ])
  
  
  
      const { stdout: flacOutput, stdin: flacInput, stderr: flacError } = spawn(
  
        "flac",
  
        ["-"]
  
      )
  
  
  
      flacOutput.on("data", (buffer: Buffer) => {
  
        totalSize += buffer.byteLength
  
      })
  
  
  
      ffmpegError.on("data", error => {
  
        console.log(error.toString())
  
      })
  
  
  
      flacError.on("data", error => {
  
        console.log(error.toString())
  
      })
  
  
  
      //stream.on("error", reject)
  
  
  
      destination.on("finish", () => {
  
        resolve({
  
          mime: "audio/flac",
  
          size: totalSize,
  
          codec: "flac",
  
          bitdepth: 16,
  
          ext: "flac"
  
        })
  
      })
  
  
  
      ffmpegOutput.pipe(flacInput)
  
      flacOutput.pipe(destination)
  
    })
  
  }

  While this code works, the resulting flac file is not correct. The source audio is of duration 06:14, but the flac file is of duration 06:45:47. Encoding the flac manually without piping ffmpeg to it works fine, but I cannot do that in a server environment where I need to utilize streams.

  Here’s what the flac encoder outputs when transcoding :

  flac 1.3.2
  
  Copyright (C) 2000-2009  Josh Coalson, 2011-2016  Xiph.Org Foundation
  
  flac comes with ABSOLUTELY NO WARRANTY.  This is free software, and you are
  
  welcome to redistribute it under certain conditions.  Type `flac' for details.
  
  
  
  -: WARNING: skipping unknown chunk 'LIST' (use --keep-foreign-metadata to keep)
  
  -: WARNING, cannot write back seekpoints when encoding to stdout
  
  -: 0% complete, ratio=0.357
  
  0% complete, ratio=0.432
  
  0% complete, ratio=0.482
  
  0% complete, ratio=0.527
  
  0% complete, ratio=0.541
  
  1% complete, ratio=0.554
  
  1% complete, ratio=0.563
  
  1% complete, ratio=0.571
  
  size=   36297kB time=00:03:30.70 bitrate=1411.2kbits/s speed= 421x
  
  1% complete, ratio=0.572
  
  1% complete, ratio=0.570
  
  1% complete, ratio=0.577
  
  1% complete, ratio=0.583
  
  1% complete, ratio=0.584
  
  1% complete, ratio=0.590
  
  1% complete, ratio=0.592
  
  size=   64512kB time=00:06:14.49 bitrate=1411.2kbits/s speed= 421x
  
  video:0kB audio:64512kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead:
  
  0.000185%
  
  
  
  -: WARNING: unexpected EOF; expected 1073741823 samples, got 16510976 samples
  
  2% complete, ratio=0.579