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• How to extract grayscale image from a video with ffmpeg-library ?

  9 mars 2016, par user1587451

  I’v compiled and tested this tutorial from here which works just fine. After I tried to edit the tutorial to read/convert frames into grayscale. I just changed pFrameRGB to pFrameGray, PIX_FMT_RGB24 to PIX_FMT_GRAY16 and to save just the 200th frame. It compiles and run but the image don’t show the expected. What’s wrong ?

  The image :
  

  The edited code :

  #include <libavcodec></libavcodec>avcodec.h>
  
  #include <libavformat></libavformat>avformat.h>
  
  #include <libswscale></libswscale>swscale.h>
  
  
  
  #include 
  
  
  
  // compatibility with newer API
  
  #if LIBAVCODEC_VERSION_INT &lt; AV_VERSION_INT(55,28,1)
  
  #define av_frame_alloc avcodec_alloc_frame
  
  #define av_frame_free avcodec_free_frame
  
  #endif
  
  
  
  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);
  
    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[]) {
  
    // Initalizing these to NULL prevents segfaults!
  
    AVFormatContext   *pFormatCtx = NULL;
  
    int               i, videoStream;
  
    AVCodecContext    *pCodecCtxOrig = NULL;
  
    AVCodecContext    *pCodecCtx = NULL;
  
    AVCodec           *pCodec = NULL;
  
    AVFrame           *pFrame = NULL;
  
    AVFrame           *pFrameGRAY = NULL;
  
    AVPacket          packet;
  
    int               frameFinished;
  
    int               numBytes;
  
    uint8_t           *buffer = NULL;
  
    struct SwsContext *sws_ctx = NULL;
  
  
  
    if(argc &lt; 2) {
  
      printf("Please provide a movie file\n");
  
      return -1;
  
    }
  
    // Register all formats and codecs
  
    av_register_all();
  
  
  
    // Open video file
  
    if(avformat_open_input(&amp;pFormatCtx, argv[1], NULL, NULL)!=0)
  
      return -1; // Couldn't open file
  
  
  
    // Retrieve stream information
  
    if(avformat_find_stream_info(pFormatCtx, NULL)&lt;0)
  
      return -1; // Couldn't find stream information
  
  
  
    // Dump information about file onto standard error
  
    av_dump_format(pFormatCtx, 0, argv[1], 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't find a video stream
  
  
  
    // Get a pointer to the codec context for the video stream
  
    pCodecCtxOrig=pFormatCtx->streams[videoStream]->codec;
  
    // Find the decoder for the video stream
  
    pCodec=avcodec_find_decoder(pCodecCtxOrig->codec_id);
  
    if(pCodec==NULL) {
  
      fprintf(stderr, "Unsupported codec!\n");
  
      return -1; // Codec not found
  
    }
  
    // Copy context
  
    pCodecCtx = avcodec_alloc_context3(pCodec);
  
    if(avcodec_copy_context(pCodecCtx, pCodecCtxOrig) != 0) {
  
      fprintf(stderr, "Couldn't copy codec context");
  
      return -1; // Error copying codec context
  
    }
  
  
  
    // Open codec
  
    if(avcodec_open2(pCodecCtx, pCodec, NULL)&lt;0)
  
      return -1; // Could not open codec
  
  
  
    // Allocate video frame
  
    pFrame=av_frame_alloc();
  
  
  
    // Allocate an AVFrame structure
  
    pFrameGRAY=av_frame_alloc();
  
    if(pFrameGRAY==NULL)
  
      return -1;
  
  
  
    // Determine required buffer size and allocate buffer
  
    numBytes=avpicture_get_size(PIX_FMT_GRAY16, pCodecCtx->width,
  
                    pCodecCtx->height);
  
    buffer=(uint8_t *)av_malloc(numBytes*sizeof(uint8_t));
  
  
  
    // Assign appropriate parts of buffer to image planes in pFrameGRAY
  
    // Note that pFrameGRAY is an AVFrame, but AVFrame is a superset
  
    // of AVPicture
  
    avpicture_fill((AVPicture *)pFrameGRAY, buffer, PIX_FMT_GRAY16,
  
           pCodecCtx->width, pCodecCtx->height);
  
  
  
    // initialize SWS context for software scaling
  
    sws_ctx = sws_getContext(pCodecCtx->width,
  
                 pCodecCtx->height,
  
                 pCodecCtx->pix_fmt,
  
                 pCodecCtx->width,
  
                 pCodecCtx->height,
  
                 PIX_FMT_GRAY16,
  
                 SWS_BILINEAR,
  
                 NULL,
  
                 NULL,
  
                 NULL
  
                 );
  
  
  
    // 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 GRAY
  
      sws_scale(sws_ctx, (uint8_t const * const *)pFrame->data,
  
            pFrame->linesize, 0, pCodecCtx->height,
  
            pFrameGRAY->data, pFrameGRAY->linesize);
  
  
  
      // Save the frame to disk
  
      if(++i==200)
  
        SaveFrame(pFrameGRAY, pCodecCtx->width, pCodecCtx->height, 
  
              i);
  
        }
  
      }
  
  
  
      // Free the packet that was allocated by av_read_frame
  
      av_free_packet(&amp;packet);
  
    }
  
  
  
    // Free the GRAY image
  
    av_free(buffer);
  
    av_frame_free(&amp;pFrameGRAY);
  
  
  
    // Free the YUV frame
  
    av_frame_free(&amp;pFrame);
  
  
  
    // Close the codecs
  
    avcodec_close(pCodecCtx);
  
    avcodec_close(pCodecCtxOrig);
  
  
  
    // Close the video file
  
    avformat_close_input(&amp;pFormatCtx);
  
  
  
    return 0;
  
  }

• convert CCTV .264 video to one of common formats (mp4, avi, etc.) via ffmpeg or other cmdline tool

  21 mars 2016, par yy502

  I’ve got a CCTV cam that produces .264 format video clips. These clips plays fine just like any other normal video recording that you would expect on portable devices, but only with it’s manufacture provided App. When played directly using VLC or mplayer, only gray blocks are visible in the picture. I doubt it is propitiatory encoding, but some kind of hardware encoded raw h264 format that I’m just lacking the right combination of arguments/options for playback or convert using ffmpeg. ffmpeg -i does report the basic metadata correctly, but also crazy amount of frame errors.... but I know the video can be played fine.

  The Android App has the following files in its lib folder :
  

  I understand these files are not all for video decoding but also some other feature in the app. I’m just hoping someone could maybe determine what extra lib or option is needed to convert it with ffmpeg. e.g. libh264ToRGB565.so could be useful maybe...?

  This is a screenshot of what to expect from the sample video.
  

  And here is the sample video clip (1.3M, 1280x720p) : http://146.185.145.75/vid.264
  (MD5 = 0ae871484b3832984f46e6820b21c673)

  Any suggestion is appreciated.

• Converting cv::Mat image from BGR to YUV using ffmpeg

  10 mars 2016, par bot1131357

  I am trying to convert BGR image into YUV420P, but when I try to view each of the YUV planes separately, this is what I see.

  Shouldn’t cv::Mat::data and AVFrame::data[0] be packed in the same way ? I should be able to do a direct memcpy. Am I missing something ?

  Any ideas ?

  Mat frame;
  
  VideoCapture cap;
  
  if(!cap.open(0)){
  
      return 0;
  
  }
  
  
  
  // capture a frame
  
  cap >> frame;
  
  if( frame.empty() ) return 0;
  
  
  
  cv::Size s = frame.size();
  
  int height = s.height;
  
  int width = s.width;
  
  
  
  // Creating two frames for conversion
  
  AVFrame *pFrameYUV =av_frame_alloc();
  
  AVFrame *pFrameBGR =av_frame_alloc();
  
  
  
  // Determine required buffer size and allocate buffer for YUV frame 
  
  int numBytesYUV=av_image_get_buffer_size(AV_PIX_FMT_YUV420P, width,
  
                  height,1);          
  
  
  
  // Assign image buffers
  
  avpicture_fill((AVPicture *)pFrameBGR, frame.data,      AV_PIX_FMT_BGR24,
  
      width, height);
  
  
  
  uint8_t* bufferYUV=(uint8_t *)av_malloc(numBytesYUV*sizeof(uint8_t));
  
  avpicture_fill((AVPicture *)pFrameYUV, bufferYUV, AV_PIX_FMT_YUV420P,
  
          width, height);
  
  
  
  // Initialise Software scaling context
  
  struct SwsContext *sws_ctx = sws_getContext(width,
  
      height,
  
      AV_PIX_FMT_BGR24,
  
      width,
  
      height,
  
      AV_PIX_FMT_YUV420P,
  
      SWS_BILINEAR,
  
      NULL,
  
      NULL,
  
      NULL
  
      );
  
  
  
  // Convert the image from its BGR to YUV
  
  sws_scale(sws_ctx, (uint8_t const * const *)pFrameBGR->data,
  
        pFrameYUV->linesize, 0, height,
  
        pFrameYUV->data, pFrameYUV->linesize);
  
  
  
  
  
  
  
  // Trying to see the different planes of YUV
  
  Mat MY = Mat(height, width, CV_8UC1);
  
  memcpy(MY.data,pFrameYUV->data[0], height*width);
  
    imshow("Test1", MY); // fail
  
  Mat MU = Mat(height/2, width/2, CV_8UC1);
  
  memcpy(MU.data,pFrameYUV->data[1], height*width/4);
  
    imshow("Test2", MU); // fail
  
  Mat MV = Mat(height/2, width/2, CV_8UC1);
  
  memcpy(MV.data,pFrameYUV->data[2], height*width/4);
  
    imshow("Test3", MV); // fail  
  
  
  
  waitKey(0); // Wait for a keystroke in the window