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• Video encoding green screen

  22 août 2016, par Mohammad Abu Musa

  I am building a screen recorder, the input stream is formatted with PP_VIDEOFRAME_FORMAT_I420 and the output is formatted with AV_PIX_FMT_YUV420P below is the code I use to do the conversion

  const uint8_t* data = static_cast<const>(frame.GetDataBuffer());
  
      pp::Size size;
  
      frame.GetSize(&amp;size);
  
      uint32_t buffersize = frame.GetDataBufferSize();
  
  
  
  
  
      if (is_recording_) {
  
          vpx_codec_iter_t iter = NULL;
  
          const vpx_codec_cx_pkt_t *pkt;
  
          // copy the pixels into our "raw input" container.
  
          int bytes_filled = avpicture_fill(&amp;pic_raw, data, AV_PIX_FMT_YUV420P, out_width, out_height);
  
          if(!bytes_filled) {
  
              Logger::Log("Cannot fill the raw input buffer");
  
              return;
  
          }
  
  
  
          if(vpx_codec_encode(&amp;codec, &amp;raw, frame_cnt, 1, flags, VPX_DL_REALTIME))
  
                die_codec(&amp;codec, "Failed to encode frame");
  
  
  
          while( (pkt = vpx_codec_get_cx_data(&amp;codec, &amp;iter)) ) {
  
              switch(pkt->kind) {
  
                  case VPX_CODEC_CX_FRAME_PKT:
  
                      glb_app_thread.message_loop().PostWork(callback_factory_.NewCallback(&amp;EncoderInstance::write_ivf_frame_header, pkt));
  
                      glb_app_thread.message_loop().PostWork(callback_factory_.NewCallback(&amp;EncoderInstance::WriteFile, pkt));
  
                      break;
  
                  default:break;
  
              }
  
          }
  
  
  
          frame_cnt++;
  
  </const>

  I have three questions :

  1- Is the conversion is done correctly ? do I have to investigate image formats more ? are data channels mapped correctly.

  2- What causes the green screen to show ? what does it mean ?

  3- Is this a thread issue ? I mean is data passed correctly and the conversion is done correctly but the threads are racing

• Unable to play mp4 file with JavaFX MediaPlayer

  20 juillet 2016, par Lennart

  I want to capture the computers screen and play resulting video with the MediaPlayer of JavaFX (jdk1.8.0_91).

  I found the supported encoding and container types and I think that mp4 with H.264/AVC and AAC is the best choice.

  I’m using FFmpeg with the DirectShow device Screen Capture Recorder to capture the screen and save the resulting video as mp4 file. I used the following command :

  ffmpeg -rtbufsize 1500M -framerate 25 -f dshow -i video="screen-capture-recorder":audio="virtual-audio-capturer" -r 25 -c:v libx264 -pix_fmt yuv420p output.mp4

  But the MediaPlayer isn’t able to play the video and throws a MediaException instead :

  MediaException: UNKNOWN : [com.sun.media.jfxmediaimpl.platform.gstreamer.GSTMediaPlayer@133b675a] ERROR_MEDIA_INVALID: ERROR_MEDIA_INVALID
  
      at javafx.scene.media.MediaException.getMediaException(MediaException.java:160)
  
      at javafx.scene.media.MediaPlayer$_MediaErrorListener.onError(MediaPlayer.java:2615)
  
      at com.sun.media.jfxmediaimpl.NativeMediaPlayer$EventQueueThread.HandleErrorEvents(NativeMediaPlayer.java:691)
  
      at com.sun.media.jfxmediaimpl.NativeMediaPlayer$EventQueueThread.run(NativeMediaPlayer.java:425)

  I previously used a video from Youtube (downloaded with some random Youtube downloader) for testing and it worked. I displayed the video codecs with the VLC player and it shows the same data (except for the frame rate and resolution) :

  
  Left is the Youtube video and right the FFmpeg output.

  Solution :
  The problem was the resolution of the video. I found an open jdk bug that says that the maximum resolution is 1920x1088 due to limitations of the used decoder. The video played fine after I scaled it.

• Stream OpenGL framebuffer over HTTP (via FFmpeg)

  17 juin 2016, par mOfl

  I have an OpenGL application of which rendered images need to be streamed over internet to mobile clients. Previously, it sufficed to simply record the rendering into a video file, which is already working, and now this should be extended to subsequent streaming.

  What is working right now :

  • Render a scene to an OpenGL framebuffer object
  • Capture the FBO content using NvIFR
  • Encode it to H.264 using NvENC (no CPU round trip required)
  • Download the encoded frame to host memory as a byte array
  • Append this frame to a video file

  None of this steps involves FFmpeg or any other library so far. I now want to replace the last step with "Stream the current frame’s byte array over internet" and I assume that using FFmpeg and FFserver would be a reasonable choice for this. Am I correct ? If not, what would be the proper way ?

  If so, how do I approach this within my C++ code ? As pointed out, the frame is already encoded. Also, there is no sound or other stuff, simply a H.264 encoded frame as byte array that is updated irregularly and should be converted into a steady video stream. I assume that this would be FFmpeg’s job and that the subsequent streaming via FFserver would be simple from there. What I don’t know is how to feed my data to FFmpeg in the first place, as all FFmpeg tutorials I found (in a non-exhaustive search) work on a file or webcam/capture device as data source, not volatile data in main memory.

  The file mentioned above that I am already able to create is a C++ file stream to which I append each single frame, meaning that different framerates of video and rendering are not treated correctly. This also needs to be taken care of at some point.

  Can somebody point me in the right direction ? Can I forward data from my application to FFmpeg to build a proper video feed without writing to the hard disk ? Tutorials are greatly appreciated. By the way FFmpeg/FFserver is not mandatory. If you have a better idea for streaming of OpenGL framebuffer contents, I’m eager to know.