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• Green screen writing FLV file libavformat

  5 mai 2013, par YYZ

  I've written a piece of C++ code that can capture webcam video frame, decode them, convert them to YUV420P, encode them and then write them to a file. If I use the mpeg2 codec and write to a .mpg file, everything works perfectly. But, if I use flv, then the output produced is just a green screen. I'm not sure if there are different encoder settings I need to set for encoding flv video ? Here's my code(the relevant parts) :

  Encoder settings :

  c->codec_id = codec_id;
  
  c->bit_rate = 400000;
  
  // Resolution must be a multiple of two.
  
  c->width    = 352;
  
  c->height   = 288;
  
  c->time_base.den = STREAM_FRAME_RATE;
  
  c->time_base.num = 1;
  
  //emit one intra frame every twelve frames at most
  
  c->gop_size      = 12;
  
  c->pix_fmt       = STREAM_PIX_FMT;

  Write the frames

  int ret;
  
  uint8_t *buffer = NULL;
  
  static struct SwsContext *sws_ctx;
  
  
  
  //Setup the codec context, and set its width and height to be equal to the input video width and height
  
  AVCodecContext *c = st->codec;
  
  c->width = pCodecCtx->width;
  
  c->height = pCodecCtx->height;
  
  
  
  av_init_packet(&packet);
  
  frameYUV = avcodec_alloc_frame();
  
  
  
  //Determine how big the buffer will need to be to store the captured frame
  
  numBytes = avpicture_get_size(STREAM_PIX_FMT,pCodecCtx->width,pCodecCtx->height);
  
  
  
  //Allocate the needed buffer size
  
  buffer = new uint8_t[numBytes];
  
  sws_ctx = sws_getContext(pCodecCtx->width,pCodecCtx->height,pCodecCtx->pix_fmt,
  
                          pCodecCtx->width,pCodecCtx->height,
  
                          STREAM_PIX_FMT,SWS_BICUBIC,NULL,NULL,NULL);
  
  
  
  //Fill the output frame
  
  avpicture_fill((AVPicture *)frameYUV,buffer,STREAM_PIX_FMT,pCodecCtx->width,pCodecCtx->height);
  
  
  
  //Read a video frame in
  
  av_read_frame(pFormatCtx,&packet);
  
  
  
  //Decode the contents of packet into pFrame
  
  avcodec_decode_video2(pCodecCtx,pFrame,&frameFinished,&packet);
  
  
  
  //Scale pFrame into frameYUV, and convert to PIXFMTYUV420P
  
  sws_scale
  
  (
  
      sws_ctx,
  
      (uint8_t const * const *)pFrame->data,
  
      pFrame->linesize,
  
      0,
  
      pCodecCtx->height,
  
      frameYUV->data,
  
      frameYUV->linesize
  
  );
  
  av_init_packet(&samsPacket);
  
  //Encode frameYUV
  
  avcodec_encode_video2(c, &samsPacket, frameYUV, &gotSamsPacket);
  
  
  
  AVPacket pkt = { 0 };
  
  int got_packet;
  
  av_init_packet(&pkt);
  
  // encode the image
  
  ret = avcodec_encode_video2(c, &pkt, frame, &got_packet);
  
  if (ret < 0){
  
      debugLogStreamSave->debug("Error encoding video frame");
  
      exit(1);
  
  }
  
  if (!ret && got_packet && pkt.size){
  
      pkt.stream_index = st->index;
  
  
  
      // Write the compressed frame to our output
  
      ret = av_interleaved_write_frame(oc, &pkt);

  Any help would be appreciated !

• How to seek in FFmpeg C/C++

  2 août 2017, par DRiFTy

  Does anyone know how to implement seeking by seconds (or milliseconds) in FFmpeg. I currently have a loop running through the frames of a video using av_read_frame() and I want to determine what time this frame should be at in seconds. If it gets to a certain point then I want to seek to a later point in the video. By the way it is not a video player, just processing the frames. Ive heard I should be able to get the dts or pts from the packet but its always returning 0.

• How to check if FFmpeg process is complete

  5 juillet 2017, par lllazo

  How can I check if ffmpeg process is complete.
  Like if I want to perform overlaying of image to video, I want to determine when the process is completed or if the output file is already complete.

  So from this command

    ffmpeg -i original.mp4 -i watermark.png -filter_complex "overlay=(W-w)/2:(H-h)/2" output.mp4

  How can I determine if output.mp4 is already complete.
  Because if I have another function to transfer the output file somewhere, the transferred file is still incomplete by the time transfer is executed.