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• Convert opencv mat frame to ffmpeg AVFrame

  1er avril 2015, par Yoohoo

  I am currently work on a c++ real-time video transmission project, now I am using opencv to capture the webcam, and I want to convert the opencv Mat to ffmepg AVFrame to do the encoding and write into buffer. At the decoder side, read packet from buffer, using ffmpeg decode, and then convert ffmpeg AVFrame to opencv Mat again and play.

  Now I have finished the opencv capturing, and I can encode v4l2 source with ffmpeg, but what I want to do is replace the v4l2 source with opencv Mat. But it get error in follow code (I just show the part of the conversion) :

      Mat opencvin;                    //frame from webcam
  
      cap.read(opencvin);
  
  
  
      Mat* opencvframe;
  
      opencvframe = &opencvin;
  
      AVFrame ffmpegout;
  
      Size frameSize = opencvframe->size();
  
      AVCodec *encoder = avcodec_find_encoder(AV_CODEC_ID_H264);
  
      AVFormatContext* outContainer = avformat_alloc_context();
  
      AVStream *outStream = avformat_new_stream(outContainer, encoder);
  
      avcodec_get_context_defaults3(outStream->codec, encoder);
  
  
  
      outStream->codec->pix_fmt = AV_PIX_FMT_YUV420P;
  
      outStream->codec->width = opencvframe->cols;
  
      outStream->codec->height = opencvframe->rows;
  
      avpicture_fill((AVPicture*)&ffmpegout, opencvframe->data, PIX_FMT_BGR24, outStream->codec->width, outStream->codec->height);
  
      ffmpegout.width = frameSize.width;
  
      ffmpegout.height = frameSize.height;

  This is a code I borrow from Internet, it seems the frame have already be encoded during conversion, before I use

  static AVCodecContext *c= NULL;
  
  
  
  c = avcodec_alloc_context3(codec);
  
  if (!c) {
  
      fprintf(stderr, "Could not allocate video codec context\n");
  
      exit(1);
  
  }
  
  c->bit_rate = 400000;
  
  /* resolution must be a multiple of two */
  
  c->width = 640;
  
  c->height = 480;
  
  /* frames per second */
  
  c->time_base= (AVRational){1,25};
  
  c->gop_size = 10; /* emit one intra frame every ten frames */
  
  c->max_b_frames=15;
  
  c->pix_fmt = AV_PIX_FMT_YUV420P; 
  
  
  
  ret = avcodec_encode_video2(c, &pkt, &ffmpegout, &got_output);

  to encode the frame. And I get core dumped error if I continue encode the converted frame.

  I want encode the frame after conversion so that I can keep the data in pkt. How can I get a pure converted ffmpeg frame from opencv frame ?

  Or if the encode have already done during coversion, how can I get the output into pkt ?

• c/c++ program for ffmpeg command line

  25 mars 2015, par Yoohoo

  I want to find the corresponding c/c++ program for the ffmpeg command line :

  ffmpeg -i sample.mp4 -an -vcodec libx264 -crf 23 outfile.h264

  which convert a sample.mp4 file to outfile.h264, and

  ffplay outfile.h264

  What I am doing is to combine the ffmpeg program with my udp socket program to do a real-time video transmission. beacause it is ’real-time’, so I want to find the ffmpeg program cut it at the frame encoding step instead of writing the frames into output file, and send frame by frame and also read frame by frame at the server side.

  My questions are :

  1.What c/c++ program is actually running when I use the above command line ?

  2.where can i find the c/c++ program ?

• How to run ffmpeg as c program

  12 mars 2015, par Yonghao Zhao

  I am a student currently work on real-time video transmission, recently I found ffmpeg command line is very powerful in real-time encoding/decoding.

  But what I want to do is move the c program of the encoding/decoding part (corresponding to ffmpeg command line) into our general big c program.

  The problem is, I have already found the corresponding c program file in ffmpeg source folder (but actually I am not sure whether it is or not) its in home/ffmpeg sources/ffmpeg/example/decoding_encoding.c.

  I opened the file but cannot run it in Codeblocks, it gives the error

  undefined reference to 'av_crc'

  and a lot of ’undefined reference’ error.

  1. Does anybody have any idea how to solve this ?
  2. And any other idea of how to trans ffmepg command line to c program ?