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• Is there a way to filter out I/B/P frames in an MPEG Video stream and access the macroblock information ?

  1er mars 2014, par Vixian

  I am trying make a program for video analysis of MPEG streams in C or C++.

  I was able to find out the frame types in a video file using

  ffprobe -show_frames -pretty File.mpg | grep 'pict_type' > pict_type.txt

  However based on the order of the frames, it seems that they are in "display" (IBBPBBP...) order not in "transmission" order (IPBBPBBPBB...) and it's not exactly ideal way of doing things as I can't assure the command didn't skip any frames or anything as it's outside of my program.

  I have tried OpenCV, but it appears the information I require is too low-level for OpenCV and I believe the solution lies in ffmpeg or libavcodec but the documentation is a nightmare past the CLI. Although I am open to other solutions !

  The information I require are :

  • The type of each frame (I, B, or P)
  • The total number of macroblocks inside a frame
  • The number of intra-coded macroblocks inside a P frame
  • The number of both forward and backward predicted macroblocks inside a B frame
  • The number of just backward predicted macroblocks inside a B frame
  • The number of just forward predircted macroblocks inside a B frame

  I would be very grateful for your help !

• Did not able to pipe output of the ffmpeg using nodejs stdout

  4 mars 2014, par rughimire

  I am not being able to pipe the output of the ffmpeg over a stdout.

  Following are the block of code what I coded so far.

      var http = require('http')
  
      , fs = require('fs') 
  
      var child_process = require("child_process")
  
  
  
      http.createServer(function (req, res) {
  
      console.log("Request:", dump_req(req) , "\n")
  
  
  
      // path of the 
  
      var path = 'test-mp4.mp4'  //test-mp4-long.mp4
  
      , stat = fs.statSync(path)
  
      , total = stat.size
  
  
  
  
  
      var range = req.headers.range
  
      , parts = range.replace(/bytes=/, "").split("-")
  
      , partialstart = parts[0]
  
      , partialend = parts[1]
  
      , start = parseInt(partialstart, 10)
  
      , end = partialend ? parseInt(partialend, 10) : total-1
  
      , chunksize = (end-start)+1
  
  
  
  
  
      console.log('RANGE: ' + start + ' - ' + end + ' = ' + chunksize +  "\n")
  
  
  
  
  
      var ffmpeg = child_process.spawn("ffmpeg",[
  
              "-i", path,             // path
  
              "-b:v" , "64k",         // bitrate to 64k
  
              "-bufsize", "64k", 
  
              "-"                     // Output to STDOUT
  
          ]);
  
  
  
  
  
      //set header
  
      res.writeHead(206
  
      , { 'Content-Range': 'bytes ' + start + '-' + end + '/' + total
  
      , 'Accept-Ranges': 'bytes', 'Content-Length': chunksize
  
      , 'Content-Type': 'video/mp4'
  
      })
  
  
  
      stdout[ params[1] ] = ffmpeg.stdout
  
  
  
      // Pipe the video output to the client response
  
      ffmpeg.stdout.pipe(res);
  
  
  
      console.log("Response", dump_res(res), "\n")
  
      }).listen(1337)

  When i replaced the ffmpeg stuffs from above code, all works fine. Following is the part of the code when i replace the ffmpeg stuffs.

   var file = fs.createReadStream(path, {start: start, end: end})

  And piping like :

  file.pipe(res)

  What wrong I am running ?

  Edit :
  The ffmpeg command works fine. I have tested this through the command line and generating proper output.

• truehd : tune VLC decoding for ARM.

  19 mars 2014, par Ben Avison

  truehd : tune VLC decoding for ARM.
  Profiling on a Raspberry Pi revealed the best performance to correspond
  
  with VLC_BITS = 5. Results for overall audio decode and the get_vlc2 function
  
  in particular are as follows :
                Before          After
  
                Mean   StdDev   Mean   StdDev  Confidence  Change
  
  6:2 total     348.8  20.1     339.6  15.1    88.8%       +2.7%  (insignificant)
  
  6:2 function  38.1   8.1      26.4   4.1     100.0%      +44.5%
  
  8:2 total     339.1  15.4     324.5  15.5    99.4%       +4.5%
  
  8:2 function  33.8   7.0      27.3   5.6     99.7%       +23.6%
  
  6:6 total     604.6  20.8     572.8  20.6    100.0%      +5.6%
  
  6:6 function  95.8   8.4      68.9   8.2     100.0%      +39.1%
  
  8:8 total     766.4  17.6     741.5  21.2    100.0%      +3.4%
  
  8:8 function  106.0  11.4     86.1   9.9     100.0%      +23.1%
  Signed-off-by : Michael Niedermayer <michaelni@gmx.at>
  

  • [DH] libavcodec/mlpdec.c