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• Save frame as image during video stream using ffmpeg, in C

  30 avril 2017, par George T.

  I’m using the Parrot SDK3 to retrieve the video stream from a Bebop2 drone. From it I need to "extract" a frame and save it as an image.

  The whole code can be found here, but I shall try to include the (what I understand as) important parts here.

  Where the video is sent to mplayer. I assume from this that the video format is h624.

  if (videoOut != NULL)
  
  {
  
      if (codec.type == ARCONTROLLER_STREAM_CODEC_TYPE_H264)
  
      {
  
          if (DISPLAY_WITH_MPLAYER)
  
          {
  
              fwrite(codec.parameters.h264parameters.spsBuffer, codec.parameters.h264parameters.spsSize, 1, videoOut);
  
              fwrite(codec.parameters.h264parameters.ppsBuffer, codec.parameters.h264parameters.ppsSize, 1, videoOut);
  
  
  
              fflush (videoOut);
  
          }
  
      }
  
  }

  Where the frame is received and written to videoOut, to be displayed

  eARCONTROLLER_ERROR didReceiveFrameCallback (ARCONTROLLER_Frame_t *frame, void *customData)
  
  {
  
      if (videoOut != NULL)
  
      {
  
          if (frame != NULL)
  
          {
  
              if (DISPLAY_WITH_MPLAYER)
  
              {
  
                  fwrite(frame->data, frame->used, 1, videoOut);
  
  
  
                  fflush (videoOut);
  
              }
  
          }
  
      }
  
      return ARCONTROLLER_OK;
  
  }

  The idea I had in mind is to fwrite(frame->data, frame->used, 1, videoOut); to a different file but that just creates a corrupted file, probably because of encoding. In what way can I get this frame and store it to a separate image ? The preferable image filetype .png, .jpg or .gif

  Any help will be greatly appreciated ! Thanks in advance !

• FFmpeg - MJPEG decoding - getting different values

  27 décembre 2016, par ahmadh

  I have a set of JPEG frames which I am muxing into an avi, which gives me a mjpeg video. This is the command I run on the console :

  ffmpeg -y -start_number 0 -i %06d.JPEG -codec copy vid.avi

  When I try to demux the video using ffmpeg C api, I get frames which are slightly different in values. Demuxing code looks something like this :

  AVFormatContext* fmt_ctx = NULL;
  
  AVCodecContext* cdc_ctx = NULL;
  
  AVCodec* vid_cdc = NULL;
  
  int ret;
  
  unsigned int height, width;
  
  
  
  ....
  
  // read_nframes is the number of frames to read
  
  output_arr = new unsigned char [height * width * 3 * 
  
                                  sizeof(unsigned char) * read_nframes];
  
  
  
  avcodec_open2(cdc_ctx, vid_cdc, NULL);
  
  
  
  int num_bytes;
  
  uint8_t* buffer = NULL;
  
  const AVPixelFormat out_format = AV_PIX_FMT_RGB24;
  
  
  
  num_bytes = av_image_get_buffer_size(out_format, width, height, 1);
  
  buffer = (uint8_t*)av_malloc(num_bytes * sizeof(uint8_t));
  
  
  
  AVFrame* vid_frame = NULL;
  
  vid_frame = av_frame_alloc();
  
  AVFrame* conv_frame = NULL;
  
  conv_frame = av_frame_alloc();
  
  
  
  av_image_fill_arrays(conv_frame->data, conv_frame->linesize, buffer, 
  
                       out_format, width, height, 1);
  
  
  
  struct SwsContext *sws_ctx = NULL;
  
  sws_ctx = sws_getContext(width, height, cdc_ctx->pix_fmt,
  
                           width, height, out_format,
  
                           SWS_BILINEAR, NULL,NULL,NULL);
  
  
  
  int frame_num = 0;
  
  AVPacket vid_pckt;
  
  while (av_read_frame(fmt_ctx, &vid_pckt) >=0) {
  
      ret = avcodec_send_packet(cdc_ctx, &vid_pckt);
  
      if (ret < 0)
  
          break;
  
  
  
      ret = avcodec_receive_frame(cdc_ctx, vid_frame);
  
      if (ret < 0 && ret != AVERROR(EAGAIN) && ret != AVERROR_EOF)
  
          break;
  
      if (ret >= 0) {
  
          // convert image from native format to planar GBR
  
          sws_scale(sws_ctx, vid_frame->data, 
  
                    vid_frame->linesize, 0, vid_frame->height, 
  
                    conv_frame->data, conv_frame->linesize);
  
  
  
          unsigned char* r_ptr = output_arr + 
  
              (height * width * sizeof(unsigned char) * 3 * frame_num);
  
          unsigned char* g_ptr = r_ptr + (height * width * sizeof(unsigned char));
  
          unsigned char* b_ptr = g_ptr + (height * width * sizeof(unsigned char));
  
          unsigned int pxl_i = 0;
  
  
  
          for (unsigned int r = 0; r < height; ++r) {
  
              uint8_t* avframe_r = conv_frame->data[0] + r*conv_frame->linesize[0];
  
              for (unsigned int c = 0; c < width; ++c) {
  
                  r_ptr[pxl_i] = avframe_r[0];
  
                  g_ptr[pxl_i]   = avframe_r[1];
  
                  b_ptr[pxl_i]   = avframe_r[2];
  
                  avframe_r += 3;
  
                  ++pxl_i;
  
              }
  
          }
  
  
  
          ++frame_num;
  
  
  
          if (frame_num >= read_nframes)
  
              break;
  
      }
  
  }
  
  
  
  ...

  In my experience around two-thirds of the pixel values are different, each by +-1 (in a range of [0,255]). I am wondering is it due to some decoding scheme FFmpeg uses for reading JPEG frames ? I tried encoding and decoding png frames, and it works perfectly fine.

  In short my goal is to get the same pixel by pixel values for each JPEG frame as I would I have gotten if I was reading the JPEG images directly. Here is the stand-alone code I used. It includes cmake files to build code, and a couple of jpeg frames with the converted avi file to test this problem. (give —filetype png to test the png decoding).

• ffmpeg is not working while uploading file using uploadify

  21 janvier 2016, par Ranjith

  for a particular video i tried like this, and it worked

  exec('/usr/bin/ffmpeg -i /home/xxxxxx/public_html/test/video1.mp4  /home/xxxxxxx/public_html/test/video1.flv');

  but for uploadify i write code like this ,

  <?php
  
  
  
  if (!empty($_FILES)) {
  
  $userId=$_SESSION["user_userid"];
  
  $filename = $_FILES['Filedata']['name'];
  
  $filetmpname = $_FILES['Filedata']['tmp_name'];
  
  $fileType = $_FILES["Filedata"]["type"];
  
  $fileSizeMB = ($_FILES["Filedata"]["size"] / 1024 / 1024);
  
  $folder=$_REQUEST['folder'];
  
  
  
  exec("/usr/bin/ffmpeg -i"."/home/xxxxxx/public_html/private/".$folder."/".$filename." "."/home/xxxxxx/public_html/private/".$folder."/".$filename.".flv");
  
  
  
  }elseif($_POST['d']){
  
  $filename = $_POST['d'];
  
  $folder=$_REQUEST['folder'];
  
  $dFile = $folder.$filename;
  
  if(file_exists($dFile)){
  
      unlink($dFile);
  
  }
  
  }
  
  ?>

  this code is not converting the uploaded file.
  help me please.

  thanks