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• How is video decoding corruption debugged ?

  20 novembre 2013, par TopGunCoder

  I just started working for a new company and my new role demands that I help debug the video corruption that they are receiving through decoding frames. As much as I intend on digging down deep into the code and looking into the specifics of my problem, it made me think about video debugging in general.

  Since handling videos is very new to me, the whole process seems pretty complex and it seems there are a lot of places for corruption to present itself. The way I see it there is at least three places where corruption could pop up (barring memory corruption from the machine) :

  • Transporting the data before it is decoded
  • decoding implementation that perpetuates corruption once it is encountered, or is all together incorrect (Which seems to be my problem)
  • Transportation to the monitor(which seems unlikely but possible)

  So what i'm really curious about is if/how people debug their video streams to determine the location of any potential corruption they are encountering. I'm sure there is no sure fire method but I am curious to see what problems are even possible and how they can be identified and triaged.

  P.S. - I'm not sure of the differences between different decoding methods but, if this question seems too vague maybe it helps to mention I am using ffmpeg and avcodec_decode_video2 for the decoding.

• Getting width and height of video using flutter

  28 avril 2019, par ebg11

  I am trying to retrieve the width and height of a video using flutter. I have tried using ffmpeg

  _flutterFFmpeg.getMediaInformation(file.path);

  but the width and height are occasionally flipped. I have noticed
  "rotate" -> "90" and "displaymatrix" -> "rotation of -90.00 degrees" are present in the meta data returned.

  Is there a bug free method of using the rotate/display matrix to determine the true width/height of the video or is there a better method/library that can help me here ?

  Thanks.

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

  30 novembre 2013, par 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.