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• advanced ffmpeg compression control

  18 juillet 2017, par Daniel Mahler

  I am using very aggressive video compression, eg -crf 51. I am using this for ’artistic’ effect, so what I am doing may not make sense from a normal video compression point of view.

  So far I have only been using very basic compression control using only the -crf or -b:v flags. The results look like ffmpeg divides images into square patches and the makes smooth approximations within the patches. This gives 2 control dimensions to the process : the patch size and the aggressiveness of the smoothing within the patches.

  It have found that ffmpeg uses both parameters to some extent, but there appears to be an absolute maximum patch size in pixels beyond which it will not go regardless of the frame size.
  After that it will only increase compression by reducing the detail within the patches.

  This is suboptimal for high resolution video, where this becomes equivalent to reducing the resolution. The problem is particularly noticeable on fractal like images which have large featureless region as well as regions of high detail.

  How can I tell ffmpeg to increase the maximum patch size and retain more detail within the patches ?

• Video streaming- control frame rate x264

  3 mars 2017, par H.A

  I’m new to video coding, I found this https://github.com/RafaelPalomar/H264LiveStreamer application code very useful to my project. I want to live stream a webcam over RTP . However, I’m having problem selecting the Frame Per Seconds (FPS). below is the function that controls the encoding param.

  void x264Encoder::initilize()
  
  {
  
    x264_param_default_preset(&parameters, "veryfast", "zerolatency");
  
    parameters.i_log_level =  X264_LOG_DEBUG;
  
    parameters.i_threads = 1;
  
    parameters.i_width = 640;
  
    parameters.i_height = 480;
  
    parameters.i_fps_num = 25;
  
    parameters.i_fps_den = 1;
  
    parameters.i_keyint_max = 25;
  
    parameters.b_intra_refresh = 1;
  
    parameters.rc.i_rc_method = X264_RC_CRF;
  
    parameters.rc.i_vbv_buffer_size = 1000000;
  
    parameters.rc.i_vbv_max_bitrate = 90000;
  
    parameters.rc.f_rf_constant = 25;
  
    parameters.rc.f_rf_constant_max = 35;
  
    parameters.i_sps_id = 7;
  
    // the following two value you should keep 1
  
    parameters.b_repeat_headers = 1;    // to get header before every I-Frame
  
    parameters.b_annexb = 1; // put start code in front of nal. we will remove start code later
  
    x264_param_apply_profile(&parameters, "baseline");
  
  
  
    encoder = x264_encoder_open(&parameters);
  
    x264_picture_alloc(&picture_in, X264_CSP_I420, parameters.i_width, parameters.i_height);
  
    picture_in.i_type = X264_TYPE_AUTO;
  
    picture_in.img.i_csp = X264_CSP_I420;
  
    // i have initilized my color space converter for BGR24 to YUV420 because my opencv video capture gives BGR24 image. You can initilize according to your input pixelFormat
  
    convertContext = sws_getContext(parameters.i_width,parameters.i_height, PIX_FMT_BGR24, parameters.i_width,parameters.i_height,PIX_FMT_YUV420P, SWS_FAST_BILINEAR, NULL, NULL, NULL);
  
  }

  I’m using VLC as client whatever number i set i_fps_num to, I always get 12-14 FPS. fore example, in VLC Codec tab shows 25 FPS but in Stream statistics tab it shows it only display 13 FPS on average. here is the X264 encoder output

  x264 [debug]: frame=  72 QP=22.24 NAL=2 Slice:P Poc:144 I:97   P:116  SKIP:987  size=1464 bytes
  
  x264 [info]: frame I:1     Avg QP:20.06  size: 17848
  
  x264 [info]: frame P:72    Avg QP:22.12  size:  1337
  
  x264 [info]: mb I  I16..4: 40.2%  0.0% 59.8%
  
  x264 [info]: mb P  I16..4:  3.1%  0.0%  2.3%  P16..4:  8.3%  2.0%  0.6%  0.0%  0.0%    skip:83.7%
  
  x264 [info]: coded y,uvDC,uvAC intra: 53.6% 46.4% 7.4% inter: 3.0% 1.6% 0.0%
  
  x264 [info]: i16 v,h,dc,p: 11% 65% 12% 12%
  
  x264 [info]: i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 15% 46% 16%  3%  4%  3%  5%  3%  6%
  
  x264 [info]: i8c dc,h,v,p: 46% 42% 10%  2%
  
  x264 [info]: kb/s:312.60

  the last frame number that was encoded is 72 while in VLC stream statistics it shows that 133 frames are Displayed and 66 blocks are decoded for 10 seconds streaming in addition the video playback is bursty.

  my question is how to change the x264 parameters to get 25 FPS ?

• Video streaming- control frame rate x264

  3 mars 2017, par H.A

  I’m new to video coding, I found this https://github.com/RafaelPalomar/H264LiveStreamer application code very useful to my project. I want to live stream a webcam over RTP . However, I’m having problem selecting the Frame Per Seconds (FPS). below is the function that controls the encoding param.

  void x264Encoder::initilize()
  
  {
  
    x264_param_default_preset(&parameters, "veryfast", "zerolatency");
  
    parameters.i_log_level =  X264_LOG_DEBUG;
  
    parameters.i_threads = 1;
  
    parameters.i_width = 640;
  
    parameters.i_height = 480;
  
    parameters.i_fps_num = 25;
  
    parameters.i_fps_den = 1;
  
    parameters.i_keyint_max = 25;
  
    parameters.b_intra_refresh = 1;
  
    parameters.rc.i_rc_method = X264_RC_CRF;
  
    parameters.rc.i_vbv_buffer_size = 1000000;
  
    parameters.rc.i_vbv_max_bitrate = 90000;
  
    parameters.rc.f_rf_constant = 25;
  
    parameters.rc.f_rf_constant_max = 35;
  
    parameters.i_sps_id = 7;
  
    // the following two value you should keep 1
  
    parameters.b_repeat_headers = 1;    // to get header before every I-Frame
  
    parameters.b_annexb = 1; // put start code in front of nal. we will remove start code later
  
    x264_param_apply_profile(&parameters, "baseline");
  
  
  
    encoder = x264_encoder_open(&parameters);
  
    x264_picture_alloc(&picture_in, X264_CSP_I420, parameters.i_width, parameters.i_height);
  
    picture_in.i_type = X264_TYPE_AUTO;
  
    picture_in.img.i_csp = X264_CSP_I420;
  
    // i have initilized my color space converter for BGR24 to YUV420 because my opencv video capture gives BGR24 image. You can initilize according to your input pixelFormat
  
    convertContext = sws_getContext(parameters.i_width,parameters.i_height, PIX_FMT_BGR24, parameters.i_width,parameters.i_height,PIX_FMT_YUV420P, SWS_FAST_BILINEAR, NULL, NULL, NULL);
  
  }

  I’m using VLC as client whatever number i set i_fps_num to, I always get 12-14 FPS. fore example, in VLC Codec tab shows 25 FPS but in Stream statistics tab it shows it only display 13 FPS on average. here is the X264 encoder output

  x264 [debug]: frame=  72 QP=22.24 NAL=2 Slice:P Poc:144 I:97   P:116  SKIP:987  size=1464 bytes
  
  x264 [info]: frame I:1     Avg QP:20.06  size: 17848
  
  x264 [info]: frame P:72    Avg QP:22.12  size:  1337
  
  x264 [info]: mb I  I16..4: 40.2%  0.0% 59.8%
  
  x264 [info]: mb P  I16..4:  3.1%  0.0%  2.3%  P16..4:  8.3%  2.0%  0.6%  0.0%  0.0%    skip:83.7%
  
  x264 [info]: coded y,uvDC,uvAC intra: 53.6% 46.4% 7.4% inter: 3.0% 1.6% 0.0%
  
  x264 [info]: i16 v,h,dc,p: 11% 65% 12% 12%
  
  x264 [info]: i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 15% 46% 16%  3%  4%  3%  5%  3%  6%
  
  x264 [info]: i8c dc,h,v,p: 46% 42% 10%  2%
  
  x264 [info]: kb/s:312.60

  the last frame number that was encoded is 72 while in VLC stream statistics it shows that 133 frames are Displayed and 66 blocks are decoded for 10 seconds streaming in addition the video playback is bursty.

  my question is how to change the x264 parameters to get 25 FPS ?