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• Encoding H.264 CBR videos with FFmpeg

  27 août 2015, par Cornstalks

  I’m trying to encode a video with ffmpeg into H.264 (via the libx264 library) with a constant bit rate. I know, I know, VBR is often preferred, but for this specific job I’m required to use CBR (just as long as it’s so many kilobytes per second ; it doesn’t have to be an exact kilobytes per frame, afaik). My sample video I’m using to test is from here : http://a1408.g.akamai.net/5/1408/1388/2005110403/1a1a1ad948be278cff2d96046ad90768d848b41947aa1986/sample_iTunes.mov.zip (it comes from http://support.apple.com/kb/HT1425)

  I can get a constant bit rate when encoding the video with MPEG-4 Video (using the commands ffmpeg -i sample_iTunes.mov -b 819968 -minrate 819968 -maxrate 819968 out.mov), and the bit rate is as expected. Reading the video’s specs via the QuickTime Inspector, it’s got a data rate of 844.94 kbit/s. Cool.

  However, when I change the codec to libx264, it seems to completely ignore my bitrate requests ! The command I’m trying is "ffmpeg -i sample_iTunes.mov -vcodec libx264 -vpre medium -b 819968 -vb 819968 -minrate 819968 -maxrate 819968 -bufsize 400000 test.mov". But when I check the video’s specs via the QuickTime Inspector, it’s got a data rate of 254.74 kbit/s. WTF ? That’s not even close !

  I’ve tried changing so many parameters and adding tons of different things, and I’ve spent 2 days googling this, but I can’t seem to get it to work. If I encode the video with the MainConcept H.264 encoder, I can get a constant bitrate, but I need this to work with ffmpeg.

  If someone can help me figure out how to do CBR H.264 encoding with FFmpeg, I will love you forever !

• Encoding H.264 CBR videos with FFmpeg

  27 août 2015, par Cornstalks

  I’m trying to encode a video with ffmpeg into H.264 (via the libx264 library) with a constant bit rate. I know, I know, VBR is often preferred, but for this specific job I’m required to use CBR (just as long as it’s so many kilobytes per second ; it doesn’t have to be an exact kilobytes per frame, afaik). My sample video I’m using to test is from here : http://a1408.g.akamai.net/5/1408/1388/2005110403/1a1a1ad948be278cff2d96046ad90768d848b41947aa1986/sample_iTunes.mov.zip (it comes from http://support.apple.com/kb/HT1425)

  I can get a constant bit rate when encoding the video with MPEG-4 Video (using the commands ffmpeg -i sample_iTunes.mov -b 819968 -minrate 819968 -maxrate 819968 out.mov), and the bit rate is as expected. Reading the video’s specs via the QuickTime Inspector, it’s got a data rate of 844.94 kbit/s. Cool.

  However, when I change the codec to libx264, it seems to completely ignore my bitrate requests ! The command I’m trying is "ffmpeg -i sample_iTunes.mov -vcodec libx264 -vpre medium -b 819968 -vb 819968 -minrate 819968 -maxrate 819968 -bufsize 400000 test.mov". But when I check the video’s specs via the QuickTime Inspector, it’s got a data rate of 254.74 kbit/s. WTF ? That’s not even close !

  I’ve tried changing so many parameters and adding tons of different things, and I’ve spent 2 days googling this, but I can’t seem to get it to work. If I encode the video with the MainConcept H.264 encoder, I can get a constant bitrate, but I need this to work with ffmpeg.

  If someone can help me figure out how to do CBR H.264 encoding with FFmpeg, I will love you forever !

• How to publish selfmade stream with ffmpeg and c++ to rtmp server ?

  25 octobre 2013, par Alexandr R

  Have a nice day to you, people !

  I am writing an application for Windows that will capture the screen and send the stream to Wowza server by rtmp (for broadcasting). My application use ffmpeg and Qt.
  I capture the screen with WinApi, convert a buffer to YUV444(because it's simplest) and encode frame as described at the file decoding_encoding.c (from FFmpeg examples) :

  ///////////////////////////
  
  //Encoder initialization
  
  ///////////////////////////
  
  avcodec_register_all();
  
  codec=avcodec_find_encoder(AV_CODEC_ID_H264);
  
  c = avcodec_alloc_context3(codec);
  
  c->width=scr_width;
  
  c->height=scr_height;
  
  c->bit_rate = 400000;
  
  int base_num=1;
  
  int base_den=1;//for one frame per second
  
  c->time_base= (AVRational){base_num,base_den};
  
  c->gop_size = 10;
  
  c->max_b_frames=1;
  
  c->pix_fmt = AV_PIX_FMT_YUV444P;
  
  av_opt_set(c->priv_data, "preset", "slow", 0);
  
  
  
  frame = avcodec_alloc_frame();
  
  frame->format = c->pix_fmt;
  
  frame->width  = c->width;
  
  frame->height = c->height;
  
  
  
  for(int counter=0;counter<10;counter++)
  
  {
  
  ///////////////////////////
  
  //Capturing Screen
  
  ///////////////////////////
  
      GetCapScr(shotbuf,scr_width,scr_height);//result: shotbuf is filled by screendata from HBITMAP
  
  ///////////////////////////
  
  //Convert buffer to YUV444 (standard formula)
  
  //It's handmade function because of problems with prepare buffer to swscale from HBITMAP
  
  ///////////////////////////
  
      RGBtoYUV(shotbuf,frame->linesize,frame->data,scr_width,scr_height);//result in frame->data
  
  ///////////////////////////
  
  //Encode Screenshot
  
  ///////////////////////////
  
      av_init_packet(&pkt);
  
      pkt.data = NULL;    // packet data will be allocated by the encoder
  
      pkt.size = 0;
  
      frame->pts = counter;
  
      avcodec_encode_video2(c, &pkt, frame, &got_output);
  
      if (got_output) 
  
      {
  
          //I think that  sending packet by rtmp  must be here!
  
          av_free_packet(&pkt);             
  
  
  
      }
  
  
  
  }
  
  // Get the delayed frames
  
  for (int got_output = 1,i=0; got_output; i++)
  
  {
  
      ret = avcodec_encode_video2(c, &pkt, NULL, &got_output);
  
      if (ret < 0)
  
          {
  
              fprintf(stderr, "Error encoding frame\n");
  
              exit(1);
  
          }
  
          if (got_output)
  
          {
  
          //I think that  sending packet by rtmp  must be here!
  
          av_free_packet(&pkt);      
  
          }
  
  }
  
  
  
  ///////////////////////////
  
  //Deinitialize encoder
  
  ///////////////////////////
  
  avcodec_close(c);
  
  av_free(c);
  
  av_freep(&frame->data[0]);
  
  avcodec_free_frame(&frame);

  I need to send video stream generated by this code to RTMP server.
  In other words, I need c++/c analog for this command :

  ffmpeg -re -i "sample.h264" -f flv rtmp://sample.url.com/screen/test_stream

  It's useful, but I don't want to save stream to file, I want to use ffmpeg libraries for realtime encoding screen capture and sending encoded frames to RTMP server inside my own application.
  Please give me a little example how to initialize AVFormatContext properly and to send my encoded video AVPackets to server.

  Thanks.