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• 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.

• ffmpeg screen blending mode with transparency

  17 novembre 2013, par gilad s

  I have a sequence of PNG files with transparency and a video- video1.mp4

  1. I'd like to convert the PNG files into a video with an alpha channel- video2.mp4

  2. I'd like to merge video2.mp4 with video1.mp4 while the transparent parts in video2 are

  not seen and the other parts are blended using screen blending mode with video1

  when I do :

  ffmpeg -i "%03d.png" -vf scale=640:480 -vcodec libx264 video2.mp4

  a video is created with a black color where the transperent parts are supposed to be (I'm not sure if it's really transparent - I tryied other encoders - all gave the same result).

  afterwards when I do :

  ffmpeg -i video1.mp4 -i video2.mp4 -filter_complex "blend=all_mode='screen'" output.mp4

  the videos are indeed merged but the video has a pink overlay ?!

• Showing a video using C (not C++ or C#)

  1er octobre 2013, par user2833591

  I learned programming in C using the Tscope-library (which is incompatible with C++ and C#), so I'm completely stuck with C.

  The Tscope-library is used to program small psychological experiments, it allows for functions that generate random numbers or produce images on the screen. Not sure if it might be a problem, but Tscope does generate it's own 'window'.

  So I wanted my experiment to show videos (currently in .wmv-format, but that can be changed, no problem), but I don't know how to do so (neither in code nor concept).

  I have come across FFmpeg, but the longer I see its code, the more I worry it's not meant for C (as in, parts of the code appear completely unknown to me). Could someone please help me ? If FFmpeg is indeed the answer, could someone give a quick run-down of the idea behind how it works (I've seen something about frames being put together) ?