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• http: cosmetics : reformat reconnect check for better readability

  11 janvier 2018, par wm4

  http: cosmetics : reformat reconnect check for better readability
  The condition was a bit too long, and most editors will break the line
  
  and turn it into an unreadable mess. Move out some of the conditions.
  This should not change the behavior.
  

  • [DH] libavformat/http.c

• Does FFMPEG apply a blur filter after scaling ?

  2 mars 2018, par Pedro Pereira

  So I am implementing my own version of bilinear scaling and comparing results with FFMPEG and ImageMagick. These tools create a scaled version of my image but it seems the results are not obtained only by applying the interpolation operations, it seems the result suffer a blur to smooth out jaggyness after the scaling.
  Here is what I mean.

  This is the original image (6x6 yuv422p) :

  https://snag.gy/Z5pa8f.jpg

  As you can see, there are only black and white columns.
  After my scaling operation with a bilinear filter I get gray columns between the black and white ones, which is expected. This is my result :

  My image (12x12 yuv422p) :

  https://snag.gy/deMJy1.jpg

  Now the problem is the result of FFMPEG. As I will show next, the FFMPEG creates an image with only a black and white column, the rest are only shades of grey which does not makes sense with bilinear filtering.

  FFMPEG image (12x12 yuv422p) :

  https://snag.gy/prz54g.jpg

  Can someone please enlight me about what FFMPEG does in this conditions ?

      // Iterate through each line
  
      for(int lin = 0; lin < dstHeight; lin++){
  
          // Get line in original image
  
          int linOrig = lin / scaleHeightRatio;
  
          float linOrigRemainder = fmod(lin, scaleHeightRatio);
  
          float linDist = linOrigRemainder / scaleHeightRatio;
  
  
  
          // For border pixels
  
          int linIndexA = linOrig;
  
          int linIndexB = linOrig + 1;
  
          if(linIndexB >= srcHeight)
  
              linIndexB = linIndexA;
  
          linIndexA *= srcWidth;
  
          linIndexB *= srcWidth;
  
  
  
          // Iterate through each column
  
          for(int col = 0; col < dstWidth; col++){
  
              // Get column in original image
  
              int colOrig = col / scaleWidthRatio;
  
              float colOrigRemainder = fmod(col, scaleWidthRatio);
  
              float colDist = colOrigRemainder / scaleWidthRatio;
  
  
  
              // If same position as an original pixel
  
              if(linOrigRemainder == 0 && colOrigRemainder == 0){
  
                  // Original pixel to the result
  
                  dstSlice[0][lin * dstWidth + col] = srcSlice[0][linOrig * srcWidth + colOrig];
  
                  dstSlice[1][lin * dstWidth + col] = srcSlice[1][linOrig * srcWidth + colOrig];
  
                  dstSlice[2][lin * dstWidth + col] = srcSlice[2][linOrig * srcWidth + colOrig];
  
  
  
                  // Continue processing following pixels
  
                  continue;
  
              }
  
  
  
              // For border pixels
  
              int colIndexA = colOrig;
  
              int colIndexB = colOrig + 1;
  
              if(colIndexB >= srcWidth)
  
                  colIndexB = colIndexA;
  
  
  
              // Perform interpolation
  
          }
  
      }

• very low latency streaminig with ffmpeg using a webcam

  5 avril, par userDtrm

  I'm trying to configure ffmpeg to do a real-time video streaming using a webcam. The ffmpeg encoder command I use is as follows.

  



  ffmpeg -f v4l2 -input_format yuyv422 -s 640x480 -i /dev/video0 -c:v libx264 -profile:v baseline -trellis 0 -subq 1 -level 32 -preset superfast -tune zerolatency -me_method epzs -crf 30 -threads 0 -bufsize 1 -refs 4 -coder 0 -b_strategy 0 -bf 0 -sc_threshold 0 -x264-params vbv-maxrate=2000:slice-max-size=1500:keyint=30:min-keyint=10: -pix_fmt yuv420p -an -f mpegts udp://192.168.1.8:5001


  



  The ffplay command used to display the video feed is,

  



  ffplay -analyzeduration 1 -fflags -nobuffer -i udp://192.168.1.8:5001


  



  However, I'm experiencing a latency of 0.5 - 1.0s latency in the video stream. Is there a way to reduce this to a number less than 100ms. Also, when I replace the v4l2 camera capture with a screen capture using x11grab, the stream is almost real-time and I experience no noticeable delays. Moreover, changing the encoder from x264 to mpeg2 had no effect on the latency. In addition, the statistics from the ffmpeg shows that the encoder is performing at a 30fps rate, which I believe indicates that the encoding is real-time. This leaves me with only one reason for the experienced delay.

  



  

  • Is there a significant delay in buffers when using v4l2 during video capturing in a webcam ?

  


  • I don't think the transmission delay is in effect in this case as I see no latencies when screen capture is used under the same conditions.

  


  • Can this latency be further reduced ?. Can someone think of a different encoder configuration to be used instead of the one that I've been using ?