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• x264/avcodec : Deduce frame sequence number from NAL unit

  4 avril 2014, par Dan Tumaykin

  I’m using avcodec H264 decoder in my project. I receive NAL units from network, stick together NALs from same frame (additional header is added on network layer) and than pass to the decoder. I was wondering if frame sequence number is encoded into NAL unit - it would be logical, as we need the reference to IDR frames.

  If this information is present - how can I extract it ?

  Right now I looking into ITU-T H.264 specification, which is quite complex I can admit. So far I have not found the answer to my question.

• c# Create NAL unit from following structure

  30 mai 2014, par user1411499

  Im wanting to send my desktop as an avc h.264 stream.

  The pseudocode would go something like :

  1) Capture screen as bitmap
  2) Encode bitmap into h.264
  3) Create NALU header
  4) Send header and payload
  5) Rinse and repeat.
  

  My questions are :
  How would I go about creating the payload ? Would I use FFMPEG to convert the Bitmap into h.264 format ?

  I have the following spec for creating the NALU :

  

  How would I go about creating this in a c# array of bytes ? (Im not that familiar with bit shifting operations) e.g ByteArray[0] = value, ByteArray1 = value

  Im fairly new to this streaming thing so any help/code samples would be great. Im not looking for references to ISO standards(I understand they are an important part), after doing a few hours of searching I found this link http://aviadr1.blogspot.co.nz/2010/05/h264-extradata-partially-explained-for.html and it was a breath of fresh air as it was someone explaining it from the beginning !

  I am also not searching for a library to do this for me as I need learn the fundamentals.

  Any help would be great thanks !

• APPLY Strong to Buffer rule. Quit Switching Bit rates MPEG DASH

  14 juillet 2015, par Vinay

  I am using mpeg dash for adaptive bit rate streaming of video from my server.

  I have used ffmpeg and MP4Box to generate 4 different quality video files from my source .mp4

  The .mpd file generated has the below code

  <?xml version="1.0"?>
  
  
  
  <mpd xmlns="urn:mpeg:dash:schema:mpd:2011" minbuffertime="PT1.500000S" type="static" mediapresentationduration="PT0H3M1.42S" profiles="urn:mpeg:dash:profile:isoff-on-demand:2011">
  
   <programinformation moreinformationurl="http://gpac.sourceforge.net">
  
    
  
   </programinformation>
  
  
  
   <period duration="PT0H3M1.42S">
  
    <adaptationset segmentalignment="true" maxwidth="1920" maxheight="1080" maxframerate="24" par="16:9" lang="und" subsegmentstartswithsap="1">
  
     <representation mimetype="video/mp4" codecs="avc1.64000d" width="320" height="240" framerate="24" sar="1:1" startwithsap="1" bandwidth="375715">
  
      <baseurl>400_dashinit.mp4</baseurl>
  
      <segmentbase indexrangeexact="true" indexrange="904-1403">
  
        <initialization range="0-903"></initialization>
  
      </segmentbase>
  
     </representation>
  
     <representation mimetype="video/mp4" codecs="avc1.640015" width="420" height="270" framerate="24" sar="1:1" startwithsap="1" bandwidth="644824">
  
      <baseurl>700_dashinit.mp4</baseurl>
  
      <segmentbase indexrangeexact="true" indexrange="905-1404">
  
        <initialization range="0-904"></initialization>
  
      </segmentbase>
  
     </representation>
  
     <representation mimetype="video/mp4" codecs="avc1.64001f" width="1024" height="576" framerate="24" sar="1:1" startwithsap="1" bandwidth="1349484">
  
      <baseurl>1500_dashinit.mp4</baseurl>
  
      <segmentbase indexrangeexact="true" indexrange="905-1404">
  
        <initialization range="0-904"></initialization>
  
      </segmentbase>
  
     </representation>
  
     <representation mimetype="video/mp4" codecs="avc1.64001f" width="1280" height="720" framerate="24" sar="1:1" startwithsap="1" bandwidth="2264379">
  
      <baseurl>2500_dashinit.mp4</baseurl>
  
      <segmentbase indexrangeexact="true" indexrange="905-1404">
  
        <initialization range="0-904"></initialization>
  
      </segmentbase>
  
     </representation>
  
     <representation mimetype="video/mp4" codecs="avc1.640028" width="1920" height="1080" framerate="24" sar="1:1" startwithsap="1" bandwidth="3633049">
  
      <baseurl>4000_dashinit.mp4</baseurl>
  
      <segmentbase indexrangeexact="true" indexrange="906-1405">
  
        <initialization range="0-905"></initialization>
  
      </segmentbase>
  
     </representation>
  
    </adaptationset>
  
   </period>
  
  </mpd>

  I am using video.js along with dash.js to playback the mpeg dash content on client side. The issue is that the video doesn’t playback perfectly when i simulate network conditions from chrome dev tools.

  It works at times and it doesn’t at others. For ex the stream starts with bit rate of 400kbps and then detects enough bandwidth available so it switches to 2500kbps. Then when i bring down my bandwidth to 400kbps again then the video freezes at some point of time.

  At times the video freezes after few initial seconds of playback when it tries to switch the stream. I think there might be some command line parameter that i am missing while generating my video files via ffmpeg or generating .mpd file via MP4Box.

  below are the commands i use for ffmpeg and MP4Box

  ffmpeg -y -i inputfile -c:a libfdk_aac -ac 2 -ab 128k -c:v libx264 -r 24 – g 24 -b:v 1500k -maxrate 1500k -bufsize 1000k -vf "scale=-1:720" outputfile.mp4
  
  
  
  
  
  MP4Box -dash [DURATION] -rap -frag-rap -profile [PROFILE] -out [path/to/outpout.file] [path/to/input1.file] [path/to/input2.file] [path/to/input3.file]

  Also while i am generating .mpd files via MP4Box i am getting below warning in console

  [DASH]: Files have non-proportional track layouts (320x240 vs 420x270) but sample size and aspect ratio match, assuming precision issue
  
  [DASH]: Files have non-proportional track layouts (320x240 vs 1024x576) but sample size and aspect ratio match, assuming precision issue
  
  [DASH]: Files have non-proportional track layouts (320x240 vs 1280x720) but sample size and aspect ratio match, assuming precision issue
  
  [DASH]: Files have non-proportional track layouts (320x240 vs 1920x1080) but sample size and aspect ratio match, assuming precision issue

  Whenever the video stops playing the chrome console has these logs

  Number of times the buffer has run dry: 25
  
  Apply STRONG to buffer rule.
  
  Quit switching bit rates.

  I don’t have any clue as to why the buffers run dry and it stops switching the bit rates.

  Anything that is predominantly wrong in the process ?