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• Patent skullduggery : Tandberg rips off x264 algorithm

  25 novembre 2010, par Dark Shikari — patents, ripoffs, x264

  Update : Tandberg claims they came up with the algorithm independently : to be fair, I can actually believe this to some extent, as I think the algorithm is way too obvious to be patented. Of course, they also claim that the algorithm isn’t actually identical, since they don’t want to lose their patent application.

  I still don’t trust them, but it’s possible it’s merely bad research (and thus being unaware of prior art) as opposed to anything malicious. Furthermore, word from within their office suggests they’re quite possibly being honest : supposedly the development team does not read x264 code at all. So this might just all be very bad luck.

  Regardless, the patent is still complete tripe, and should never have been filed.
  

  Most importantly, stop harassing the guy whose name is on the patent (Lars) : he’s just a programmer, not the management or lawyers responsible for filing the patent. This is stupid and unnecessary. I’ve removed the original post because of this ; it can be found here for those who want to read it.

  Appendix : the details of the patent :

  I figure I’ll go over the exact correspondence between the patent and my code here.

  1. A method for calculating run and level representations of quantized transform coefficients representing pixel values included in a block of a video picture, the method comprising :

  Translation : It’s a run-level coder.

  packing, at a video processing apparatus, each quantized transform coefficients in a value interval [Max, Min] by setting all quantized transform coefficients greater than Max equal to Max, and all quantized transform coefficients less than Min equal to Min

  The quantized coefficients are clipped to a certain valid range to allow them to be packed into bytes (they start as 16-bit values).

  reordering, at the video processing apparatus, the quantized transform ID coefficients according to a predefined order depending on respective positions in the block resulting in an array C of reordered quantized transform coefficients

  This is the zigzag pattern used in H.264 (and most formats) for reordering DCT coefficients. In x264, this is done before the run-level coder ste.

  masking, at the video processing apparatus, C by generating an array M containing ones in positions corresponding to positions of C having non-zero values, and zeros in positions corresponding to positions of C having zero values

  This is creating a bitmask based on the coefficient values, the pmovmskb step.

  is generating, at the video processing apparatus, for each position containing a one in M, a run and a level representation by setting the level value equal to an occurring value in a corresponding position of C ; and setting, at the video processing apparatus, for each position containing a one in M₅ the run value equal to the number of proceeding positions relative to a current position in M since a previous occurrence of one in M.

  This is the process of creating run/level values from the bitmask.

  Now into the detailed claims :

  2. The method according to Claim 1, wherein the masking further includes, creating an array C from C where positions corresponding to positions of nonzero values in C are filled with ones, and positions corresponding to positions of zero values in C are filled with zeros, and creating M from C by extracting the most significant bit from values in respective position of C and inserting the bits in corresponding positions in M.

  They’re extracting the most significant bit of the values to create a bitmask. This is exactly what the pmovmskb in my algorithm does.

  3. The method according to Claim 2, wherein the creating of the array C is executed by a C++ function PCMPGTB, and the creating of M from C is executed by a C++ function PMOVMSKB.

  And here they use pcmpgtb (they call it a C++ function for some reason, but it’s a SSE instruction) to do the clipping of the input values. This is exactly the same method I used in decimate_score. They also use pmovmskb as mentioned.

  4. The method according to Claim 1 , wherein the generating of the run and level representation further includes determining positions containing non-zero values in C by corresponding positions containing ones in M.

  5. The method according to Claim 4, wherein the determining of positions containing non-zero values in C is executed by a C++ function BSF.

  Here they iterate over the bitmask of transform coefficients using a “BSF” function to find runs, which is exactly what I did. Of course, BSF isn’t a function, it’s an x86 instruction.

  6. The method according to Claim 1 , wherein Max is 256 and Min is 0.

  This is almost surely a typo or mistake of some sort. They mean the Max should be 255, not 256 : 256 doesn’t fit in a uint8_t.

  7. The method according to Claim 1 , wherein the predefined order follows a zigzag path of transform coefficient positions in the block starting in an upper left corner heading towards a lower right corner.

  This is a description of the typical DCT zigzag pattern (like in H.264, MPEG-2, Theora, etc).

  Everything after this part is just repeating itself with the phrase “an apparatus” added in order to make the USPTO listen to them.

• Picturebox from AForge FFMPEG empty - C#/WinForms

  1er août 2017, par Jake Delson

  I’ve done a ton of research and looked at a lot of questions here but can’t seem to find anything to help me. I should preface I’m very new to C#, Windows Forms, and SO ! I’m a 1st year CompSci student coming from C++ experimenting with my own projects for the summer. I’m trying to display a series of bitmaps from a .avi using the AForge.Video.FFMPEG video file reader.

  It seems to be finding the file, getting its’ data (console prints dimensions, framerate, and codec) and creating the picturebox, but the picturebox comes up blank/empty. I get the bitmap from the frames of a .avi :

  From AForge example code here

  Then I’m trying to display it with a picture box :

  From MS example code here as well

  And here’s my code. Essentially a combination of the two :

      public class Simple : Form
  
  {
  
      Bitmap videoFrame;
  
  
  
      public Simple()
  
      {
  
          try
  
          {
  
              // create instance of video reader
  
              VideoFileReader reader = new VideoFileReader();
  
              // open video file
  
              reader.Open(@"C:\Users\User\Desktop\ScanTest3.AVI");
  
              // check some of its attributes
  
              Console.WriteLine("width:  " + reader.Width);
  
              Console.WriteLine("height: " + reader.Height);
  
              Console.WriteLine("fps:    " + reader.FrameRate);
  
              Console.WriteLine("codec:  " + reader.CodecName);
  
  
  
              PictureBox pictureBox1 = new PictureBox();
  
  
  
              // read 100 video frames out of it
  
              for (int i = 0; i < 100; i++)
  
              {
  
                  videoFrame = reader.ReadVideoFrame();
  
  
  
                  pictureBox1.SizeMode = PictureBoxSizeMode.StretchImage;
  
                  pictureBox1.ClientSize = new Size(videoFrame.Width, videoFrame.Height);
  
                  pictureBox1.Image = videoFrame;
  
  
  
                  // dispose the frame when it is no longer required
  
                  videoFrame.Dispose();
  
              }
  
  
  
              reader.Close();
  
          }
  
  
  
          catch
  
          {
  
              Console.WriteLine("Nope");
  
          }
  
  
  
      }
  
  }
  
  
  
  class MApplication
  
  {
  
      public static void Main()
  
      {
  
          Application.Run(new Simple());
  
      }
  
  }

  So that’s it pretty much. Just a blank picture box coming up, when it should have the first frame of the video, even though no exception caught (though I’m pretty confident I’m using the try/catch very poorly), and the console printing the correct data for the file :

  width:  720
  
  height: 480
  
  fps:    29
  
  codec:  dvvideo
  
  [swscaler @ 05E10060] Warning: data is not aligned! This can lead to a speedloss

  Though if anyone could tell me what that warning means, that would be great as well, but I’m mainly just lost as to why there’s no picture printing to the screen.

  Thanks !

• avutil/mathematics : speed up av_gcd by using Stein’s binary GCD algorithm

  11 octobre 2015, par Ganesh Ajjanagadde

  avutil/mathematics : speed up av_gcd by using Stein’s binary GCD algorithm
  This uses Stein’s binary GCD algorithm :
  
  https://en.wikipedia.org/wiki/Binary_GCD_algorithm
  
  to get a roughly 4x speedup over Euclidean GCD on standard architectures
  
  with a compiler intrinsic for ctzll, and a roughly 2x speedup otherwise.
  
  At the moment, the compiler intrinsic is used on GCC and Clang due to
  
  its easy availability.
  Quick note regarding overflow : yes, subtractions on int64_t can, but the
  
  llabs takes care of that. The llabs is also guaranteed to be safe, with
  
  no annoying INT64_MIN business since INT64_MIN being a power of 2, is
  
  shifted down before being sent to llabs.
  The binary GCD needs ff_ctzll, an extension of ff_ctz for long long (int64_t). On
  
  GCC, this is provided by a built-in. On Microsoft, there is a
  
  BitScanForward64 analog of BitScanForward that should work ; but I can’t confirm.
  
  Apparently it is not available on 32 bit builds ; so this may or may not
  
  work correctly. On Intel, per the documentation there is only an
  
  intrinsic for _bit_scan_forward and people have posted on forums
  
  regarding _bit_scan_forward64, but often their documentation is
  
  woeful. Again, I don’t have it, so I can’t test.
  As such, to be safe, for now only the GCC/Clang intrinsic is added, the rest
  
  use a compiled version based on the De-Bruijn method of Leiserson et al :
  
  http://supertech.csail.mit.edu/papers/debruijn.pdf.
  Tested with FATE, sample benchmark (x86-64, GCC 5.2.0, Haswell)
  
  with a START_TIMER and STOP_TIMER in libavutil/rationsl.c, followed by a
  
  make fate.
  aac-am00_88.err :
  
  builtin :
  
  714 decicycles in av_gcd,    4095 runs,      1 skips
  de-bruijn :
  
  1440 decicycles in av_gcd,    4096 runs,      0 skips
  previous :
  
  2889 decicycles in av_gcd,    4096 runs,      0 skips
  Signed-off-by : Ganesh Ajjanagadde <gajjanagadde@gmail.com>
  
  Signed-off-by : Michael Niedermayer <michael@niedermayer.cc>
  

  • [DH] libavutil/intmath.h
  • [DH] libavutil/mathematics.c