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• Capture JPEG frame from avi file using ffmpeg library. How to open captured files?

  30 November 2013, by ios198

  This is the code I found from the ffmpeg tutorial website:

  #include <libavcodec></libavcodec>avcodec.h>
  
  #include <libavformat></libavformat>avformat.h>
  
  #include <libswscale></libswscale>swscale.h>
  
  #include 
  
  void SaveFrame(AVFrame *pFrame, int width, int height, int iFrame) {
  
    FILE *pFile;
  
    char szFilename[32];
  
    int  y;
  
  
  
    // Open file
  
    sprintf(szFilename, "frame%d.ppm", iFrame); // szFilenam = frame4.ppm
  
    pFile=fopen(szFilename, "wb");
  
    if (pFile == NULL) {
  
     return;
  
      } 
  
     //Write header
  
    fprintf(pFile, "P6\n%d %d\n255\n", width, height);
  
  
  
    // Write pixel data
  
    for(y=0; ydata[0]+y*pFrame->linesize[0], 1, width*3, pFile);
  
  
  
    // Close file
  
    fclose(pFile);
  
  }
  
  
  
  int main(int argc, char **argv[])
  
  {
  
      AVFormatContext *pFormatCtx = NULL;
  
      int             i, videoStream;
  
      AVCodecContext  *pCodecCtx = NULL;
  
      AVCodec         *pCodec = NULL;
  
      AVFrame         *pFrame = NULL; 
  
      AVFrame         *pFrameRGB = NULL;
  
      AVPacket        packet;
  
      int             frameFinished;
  
      int             numBytes;
  
      uint8_t         *buffer = NULL;
  
  
  
      AVDictionary    *optionsDict = NULL;
  
      struct SwsContext      *sws_ctx = NULL;
  
  
  
  
  
      // Register all formats and codecs
  
      av_register_all();
  
  
  
      // Open video file
  
      if(avformat_open_input(&amp;pFormatCtx, "/root/dhquan/AVI/turning_pages.avi", NULL, NULL)!=0)
  
          return -1; // couldn&#39;t open file
  
  
  
      // Retrieve stream information
  
      if(avformat_find_stream_info(pFormatCtx,NULL)&lt;0)
  
          return -1; // couldn&#39;t find stream information
  
                     // This function populates pFormatCtx->streams with the proper 
  
  
  
      // dump information about file onto standard error
  
      av_dump_format(pFormatCtx, 0, "/root/dhquan/AVI/turning_pages.avi", 0);
  
  
  
      // Find the first video stream
  
      videoStream = -1;
  
      for(i=0;inb_streams;i++)
  
          if(pFormatCtx->streams[i]->codec->codec_type==AVMEDIA_TYPE_VIDEO){
  
              videoStream=i;
  
              break;
  
          }
  
          if(videoStream==-1)
  
              return -1; // didn&#39;t find a video stream
  
  
  
      // Get a pointer to the codec context for the video stream
  
          pCodecCtx= pFormatCtx->streams[videoStream]->codec;
  
  
  
      // Find the decoder for the video stream
  
          pCodec=avcodec_find_decoder(pCodecCtx->codec_id);
  
          if(pCodec==NULL){
  
              fprintf(stderr,"Unsupported codec!\n");
  
              return -1;
  
          }
  
  
  
      // Open Codec
  
          if(avcodec_open2(pCodecCtx, pCodec, &amp;optionsDict)&lt;0)
  
              return -1; // Could not open codec
  
  
  
      // Allocate video frame
  
          pFrame = avcodec_alloc_frame();
  
  
  
      // Allocate an AVFrame structure
  
           pFrameRGB=avcodec_alloc_frame();
  
          if(pFrameRGB==NULL)
  
              return -1;
  
      // Determine required buffer size and allocate buffer
  
           numBytes=avpicture_get_size(PIX_FMT_RGB24, pCodecCtx->width,
  
                    pCodecCtx->height);
  
           buffer=(uint8_t *)av_malloc(numBytes*sizeof(uint8_t));
  
  
  
           sws_ctx =
  
           sws_getContext
  
      (
  
          pCodecCtx->width,
  
          pCodecCtx->height,
  
          pCodecCtx->pix_fmt,
  
          pCodecCtx->width,
  
          pCodecCtx->height,
  
          PIX_FMT_RGB24,
  
          SWS_BILINEAR,
  
          NULL,
  
          NULL,
  
          NULL
  
      );
  
  
  
    // Assign appropriate parts of buffer to image planes in pFrameRGB
  
    // Note that pFrameRGB is an AVFrame, but AVFrame is a superset
  
    // of AVPicture
  
    avpicture_fill((AVPicture *)pFrameRGB, buffer, PIX_FMT_RGB24,
  
           pCodecCtx->width, pCodecCtx->height);
  
  
  
    // Read frames and save first five frames to disk
  
    i=0;
  
    while(av_read_frame(pFormatCtx, &amp;packet)>=0) {
  
      // Is this a packet from the video stream?
  
      if(packet.stream_index==videoStream) {
  
        // Decode video frame
  
        avcodec_decode_video2(pCodecCtx, pFrame, &amp;frameFinished, 
  
                 &amp;packet);
  
  
  
        // Did we get a video frame?
  
        if(frameFinished) {
  
      // Convert the image from its native format to RGB
  
          sws_scale
  
          (
  
              sws_ctx,
  
              (uint8_t const * const *)pFrame->data,
  
              pFrame->linesize,
  
              0,
  
              pCodecCtx->height,
  
              pFrameRGB->data,
  
              pFrameRGB->linesize
  
          );
  
  
  
      // Save the frame to disk
  
      if(++i&lt;=5)
  
        SaveFrame(pFrameRGB, pCodecCtx->width, pCodecCtx->height, 
  
              i);
  
        }
  
      }
  
  
  
      // Free the packet that was allocated by av_read_frame
  
      av_free_packet(&amp;packet);
  
    }
  
  
  
    // Free the RGB image
  
    av_free(buffer);
  
    av_free(pFrameRGB);
  
  
  
    // Free the YUV frame
  
    av_free(pFrame);
  
  
  
    // Close the codec
  
    avcodec_close(pCodecCtx);
  
  
  
    // Close the video file
  
    avformat_close_input(&amp;pFormatCtx);
  
  
  
    return 0;
  
    //getch();
  
  }

  In line :
  sprintf(szFilename, "frame%d.ppm", iFrame);

  I changed into frame%d.jpg. It creates .jpg file in my folder. But I can't read it. How to open this file? Please help me.

• Revision ab4c6efa48: Merge "Optimize the code to set the refernce frame right after reading the heade

  10 October 2014, by hkuang

  Merge "Optimize the code to set the refernce frame right after reading the
  header."

• Revision 3304d4e6ca: Optimize the code to set the refernce frame right after reading the header. Cha

  10 October 2014, by hkuang

  Changed Paths:
   Modify /vp9/decoder/vp9_decodeframe.c

  
   Modify /vp9/decoder/vp9_decodemv.c

  
  
  Optimize the code to set the refernce frame right after reading the header.

  Change-Id: I495cf4a366e06e3220ed132500b1ba1c8448f708