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• What does "dash" - mean as ffmpeg output filename

  26 août 2020, par DDS

  I'm trying to use ffmpeg with gnuplot to draw some audio spectra, I'm following this ffmpeg doc link.

  


  Now I'm asking what "dash" - means on this line right after -f data, it should be a filename : the last element of ffmpeg command should the output file but I have no files named - in the directory after running the command.

  


  ffmpeg -y -i in.wav -ac 1 -filter:a aresample=8000 -map 0:a -c:a pcm_s16le -f data - | gnuplot -p -e "plot 'code>

  


  I looked on ffmpeg docs but I didn't find anything.

  


• 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)

• Playing 'aes-256-ctr' encrypted DASH stream with FFMPEG/FFPLAY

  9 mars 2020, par michalSolarz

  I try to play that stream with following command ffplay  -allowed_extensions ALL -loglevel debug -decryption_key "***" -encryption_scheme aes-256-ctr  https://*** but I receive following output :

   Error when loading first fragment, playlist 0
  
  [AVIOContext @ 0x7f6a60647600] Statistics: 55123 bytes read, 0 seeks
  
  ****/stream.mpd: Invalid data found when processing input

  Is it possible to do it at all ?