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• How do I keep black areas black with ffmpeg ?

  11 janvier 2018, par Aurelius Schnitzler

  When encoding GoPro videos with ffmpeg using

  ffmpeg -i Goprovideo.mp4 -pix_fmt yuv420p -vf scale=1920:-1,crop=1920:1080:0:362 Goprovideo-out.mp4

  I noticed that the videos do not only get much smaller, but also in some cases do black areas lose intensity. So what was black is now grey. Not to an extreme, but slightly noticable.

  How do I keep black areas black with ffmpeg ?

• libx264 encoder video plays too fast

  23 avril 2014, par Nick

  I’m trying to write a program that uses libx264 to encode the video frames. I’ve wrapped this code into a small class (see below). I have frames that are in YUV420 format. libx264 encodes the frames and I save them to a file. I can play the file back in VLC, all of the frames are there, but it plays back at several hundred times the actual frame rate. Currently I am capturing frames at 2.5 FPS, but they play back as if it was recorded at 250 or more FPS. I’ve tried to change the frame rate with no luck.

  I’ve also tried to set

  _param.b_vfr_input = 1

  and then set the time bases appropriately, but that causes my program to crash. Any ideas ? My encode code is shown below. I’ve also included the output of ffprobe -show_frames

  Wrapper Class :

  x264wrapper::x264wrapper(int width, int height, int fps, int timeBaseNum, int timeBaseDen, int vfr)
  
  {
  
      x264_param_default_preset(&_param, "veryfast", "zerolatency");
  
      _param.i_threads = 1;
  
      _param.i_width = width;
  
      _param.i_height = height;
  
      _param.i_fps_num = fps;
  
      _param.i_fps_den = 1;
  
      // Intra refres:
  
      _param.i_keyint_max = fps;
  
      _param.b_intra_refresh = 1;
  
      //Rate control:
  
      _param.rc.i_rc_method = X264_RC_CRF;
  
      //_param.rc.i_rc_method = X264_RC_CQP;
  
      _param.rc.f_rf_constant = 25;
  
      _param.rc.f_rf_constant_max = 35;
  
      //For streaming:
  
      _param.b_repeat_headers = 1;
  
      _param.b_annexb = 1;    
  
      // misc
  
      _param.b_vfr_input = vfr;
  
      _param.i_timebase_num = timeBaseNum; 
  
      _param.i_timebase_den = timeBaseDen;
  
  
  
      _param.i_log_level = X264_LOG_DEBUG;
  
  
  
      _encoder = x264_encoder_open(&_param);
  
  
  
      cout << "Timebase " << _param.i_timebase_num << "/" << _param.i_timebase_den << endl;
  
      cout << "fps " << _param.i_fps_num << "/" << _param.i_fps_den << endl;
  
      _ticks_per_frame = (int64_t)_param.i_timebase_den * _param.i_fps_den / _param.i_timebase_num / _param.i_fps_num;
  
      cout << "ticks_per_frame " << _ticks_per_frame << endl;
  
      int result = x264_picture_alloc(&_pic_in, X264_CSP_I420, width, height);
  
      if (result != 0)
  
      {
  
          cout << "Failed to allocate picture" << endl;
  
          throw(1);
  
      }
  
  
  
      _ofs = new ofstream("output.h264", ofstream::out | ofstream::binary);
  
      _pts = 0;
  
  }
  
  
  
  
  
  x264wrapper::~x264wrapper(void)
  
  {
  
      _ofs->close();
  
  }
  
  
  
  
  
  
  
  void x264wrapper::encode(uint8_t * buf)
  
  {
  
      x264_nal_t* nals;
  
      int i_nals;
  
      convertFromBalserToX264(buf);
  
      _pts += _ticks_per_frame;
  
      _pic_in.i_pts = _pts;
  
      x264_picture_t pic_out;
  
      int frame_size = x264_encoder_encode(_encoder, &nals, &i_nals, &_pic_in, &pic_out);
  
      if (frame_size >= 0)
  
      {
  
          _ofs->write((char*)nals[0].p_payload, frame_size);
  
      }
  
      else
  
      {
  
          cout << "error: x264_encoder_encode failed" << endl;
  
      }
  
  }

  Output of ffprobe -show_frames :

  [FRAME]
  
  media_type=video
  
  key_frame=1
  
  pkt_pts=N/A
  
  pkt_pts_time=N/A
  
  pkt_dts=N/A
  
  pkt_dts_time=N/A
  
  pkt_duration=48000
  
  pkt_duration_time=0.040000
  
  pkt_pos=0
  
  width=1920
  
  height=1080
  
  pix_fmt=yuv420p
  
  sample_aspect_ratio=N/A
  
  pict_type=I
  
  coded_picture_number=0
  
  display_picture_number=0
  
  interlaced_frame=0
  
  top_field_first=0
  
  repeat_pict=0
  
  reference=0
  
  [/FRAME]
  
  [FRAME]
  
  media_type=video
  
  key_frame=0
  
  pkt_pts=N/A
  
  pkt_pts_time=N/A
  
  pkt_dts=N/A
  
  pkt_dts_time=N/A
  
  pkt_duration=N/A
  
  pkt_duration_time=N/A
  
  pkt_pos=54947
  
  width=1920
  
  height=1080
  
  pix_fmt=yuv420p
  
  sample_aspect_ratio=N/A
  
  pict_type=P
  
  coded_picture_number=1
  
  display_picture_number=0
  
  interlaced_frame=0
  
  top_field_first=0
  
  repeat_pict=0
  
  reference=0
  
  [/FRAME]
  
  [FRAME]
  
  media_type=video
  
  key_frame=0
  
  pkt_pts=N/A
  
  pkt_pts_time=N/A
  
  pkt_dts=N/A
  
  pkt_dts_time=N/A
  
  pkt_duration=N/A
  
  pkt_duration_time=N/A
  
  pkt_pos=57899
  
  width=1920
  
  height=1080
  
  pix_fmt=yuv420p
  
  sample_aspect_ratio=N/A
  
  pict_type=P
  
  coded_picture_number=2
  
  display_picture_number=0
  
  interlaced_frame=0
  
  top_field_first=0
  
  repeat_pict=0
  
  reference=0
  
  [/FRAME]

• setting bit rates in creating video from images in ffmpeg not working

  2 mai 2014, par mast kalandar

  I have a HQ video of one second

  Some information of this video is as below

  Dimensions : 1920 x 1080    
  
  Codec : H.264    
  
  Framerate : 30 frames per second    
  
  Size : 684.7 kB (6,84,673 bytes)
  
  Bitrates : 5458 kbps

  I have extracted frames from video

  ffmpeg -i f1.mp4 f%d.jpg

  All images are of 1920 x 1020 pixels by default 30 frames are generated (f7_1.jpg, f7_2.jpg,.....,f7_30.jpg)

  I have added some texts and objects to these images (without changing dimensions of any image, all 30 images are still of 1920 x 1020 pixels)

  Now I am trying to merge all these images to create single video (of 1 second)

  I referred this official document, I have run below command

  ffmpeg -f image2 -i f7_%d.jpg -r 30 -b:v 5458k foo_5458_2.mp4

  Video created is also of one second, thing is its bit rates are higher then the original one. New video has 6091 kbps bit rates, while I expect are 5458 kbps only.

  Because of higher bits, its gets finish very quickly compare to original video in video player.

  Is there any thing I missing ??

  And I don’t know what is exact meaning and job of -f image2 option, when I run command without this option, I am getting same video.