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• How to force avcodec to use unaligned frame data planes ?

  26 février 2015, par user3244284

  I have been searching high and low for an option to force avcodec to use unaligned memory for its AVFrame data.

  Depending on the pixel format, the horizontal planes of an AVFrame->data may be padded with extra data to be aligned to memory for performance.

  eg : a 1920 * 1080 video with 4 bytes per pixel will have 1920 * 4 = 7680 bytes per plane.

  With avcodec if you are decoding this video it will create 7808 bytes per plane.

  This adds 7808 - 7680 = 128 bytes of extra padding.

  For my purposes I would like to force avcodec to use unaligned data so I can copy an entire continuous chunk of frame data instead of copying and formatting smaller pieces one at a time to a continuous chunk.

  The following flag found in the headers :

  /* encoding support
  
     These flags can be passed in AVCodecContext.flags before initialization.
  
     Note: Not everything is supported yet.
  
  */
  
  
  
  /**
  
   * Allow decoders to produce frames with data planes that are not aligned
  
   * to CPU requirements (e.g. due to cropping).
  
   */
  
  #define CODEC_FLAG_UNALIGNED 0x0001

  Setting this AVCodecContext.flags to be CODEC_FLAG_UNALIGNED, the assumption is that the AVFrame->data is now unaligned, this is not the case.

  I’m not sure if I am looking at the right place or using this flag correctly.

  Regards,

  Curious George

• X264 Error message when capturing video

  2 mai 2015, par sav

  I’m writing a program to save some webcam video to a file. I’m using the x264 codec found here
  x264

  When I try writing frames to a file I get this error message poping up.
  

  x264vfw [warning] : Few frames probably would be lost. Ways to fix
  this :

  x264vfw [warning] : -if you use VirtualDub or its fork than you can
  enable ’VirtualDub Hack’ option

  x264vfw [warning] : -you can enable ’File’ output mode

  x264vfw [warning] : -you can enable ’Zero Latency’ option

  I found this VirtualDub Hack but then I’m not using virtual dub.
  I’m not sure what the File output mode and zero latency mean.

  I think the problem is related to the codec since when I change to using a different codec, everything works fine. I’m using C# and emgu but I dont think thats where the problem lies.

  EDIT

  In case the code helps

  public static void StartCapture()
  
  {
  
      try
  
      {
  
          capture = new Capture();
  
          capture.SetCaptureProperty(Emgu.CV.CvEnum.CAP_PROP.CV_CAP_PROP_FRAME_WIDTH, 1920);  //1920
  
          capture.SetCaptureProperty(Emgu.CV.CvEnum.CAP_PROP.CV_CAP_PROP_FRAME_HEIGHT, 1080); //1080
  
  
  
          CaptureOutput = new VideoWriter
  
          (
  
              "capture output.avi",
  
              CvInvoke.CV_FOURCC('X','2','6','4'),
  
              50, //fps
  
              (int)capture.GetCaptureProperty(Emgu.CV.CvEnum.CAP_PROP.CV_CAP_PROP_FRAME_WIDTH), 
  
              (int)capture.GetCaptureProperty(Emgu.CV.CvEnum.CAP_PROP.CV_CAP_PROP_FRAME_HEIGHT), 
  
              true
  
          );
  
  
  
          if (capture != null)
  
          {
  
              capture.ImageGrabbed += SaveFrame;
  
              capture.Start();
  
          }
  
      }
  
      catch (Exception e)
  
      {
  
          MessageBox.Show(e.ToString());
  
      }
  
  }
  
  
  
  static void SaveFrame(System.Object sender, EventArgs e)
  
  {
  
      Image video;
  
      video = capture.RetrieveBgrFrame();
  
      CaptureOutput.WriteFrame(video);
  
  }

• Trouble concatenating with ffmpeg (threads)

  4 janvier 2014, par mistypants

  I'm writing a batch script to automate one of my video editing processes. I've gotten everything done up to the final step, when I concatenate the video intro (1080.avi) with the video itself, then output. Here's the concatenate part of the script :

  ffmpeg -i 1080.avi -i %input%-lossless.avi ^
  
  -filter_complex "[0:0] [0:1] [1:0] [1:1] concat=n=2:v=1:a=1 [v] [a]" ^
  
  -map "[v]" -map "[a]" ^
  
  -c:v libx264 -preset veryslow -pix_fmt yuv420p ^
  
  -b:a 160k ^
  
  -threads 2 %input%-final.mp4

  It seems to work fine, but my computer overheats (it's a laptop) while it runs. I had this problem with just simple conversions and ffmpeg, so I added the -threads 2 part which eliminated the problem. It's back now.

  Did I mess up something in the script, or does concatenating just use more of the CPU ? If the latter, could I just decrease it to 1 thread ?