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• How to paint on a video frame by frame and save it using flutter ?

  20 septembre 2022, par Maxence Bourdin

  The goal is to analyse a video frame by frame and apply a painting on each of those frames. Then save the video and be able to play it.

  


  Do you know if such a thing is possible in flutter ? I've heard about ffmpeg package but I'm not too sure if that's possible with it.

  


• How to save image from the middle of a video ?

  29 octobre 2017, par puppon -su

  I need to make a thumbnail for a video, to seek to the 25% of a video and save the image. Here is what I’m doing right now, but it only saves black image.

  #include 
  
  
  
  #include <libavformat></libavformat>avformat.h>
  
  #include <libavutil></libavutil>dict.h>
  
  
  
  int main (int argc, char **argv)
  
  {
  
  
  
      av_register_all();
  
  
  
      AVFormatContext *pFormatCtx = avformat_alloc_context();
  
  
  
      int res;
  
  
  
      res = avformat_open_input(&amp;pFormatCtx, "test.mp4", NULL, NULL);
  
      if (res) {
  
          return res;
  
      }
  
  
  
  
  
      avformat_find_stream_info(pFormatCtx, NULL);
  
  
  
      int64_t duration = pFormatCtx->duration;
  
  
  
  
  
      // Find the first video stream
  
      int videoStream=-1;
  
      for(int i=0; inb_streams; i++) {
  
          if(pFormatCtx->streams[i]->codec->codec_type==AVMEDIA_TYPE_VIDEO) {
  
              videoStream=i;
  
              break;
  
          }
  
      }
  
      if(videoStream==-1) {
  
          return -1;
  
      }
  
  
  
      AVCodecContext *pCodecCtxOrig = NULL;
  
  
  
      // Get a pointer to the codec context for the video stream
  
      pCodecCtxOrig=pFormatCtx->streams[videoStream]->codec;
  
  
  
  
  
      AVCodec *pCodec = NULL;
  
      // 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
  
      }
  
  
  
  
  
      AVCodecContext *pCodecCtx = NULL;
  
      // 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
  
      }
  
  
  
  
  
      AVFrame *pFrame = NULL;
  
  
  
      pFrame=av_frame_alloc();
  
  
  
      AVFrame *pFrameRGB = NULL;
  
  
  
      pFrameRGB=av_frame_alloc();
  
  
  
  
  
  
  
      // Determine required buffer size and allocate buffer
  
      int numBytes=avpicture_get_size(AV_PIX_FMT_RGB24, pCodecCtx->width,
  
                                  pCodecCtx->height);
  
  
  
      uint8_t *buffer = NULL;
  
      buffer=(uint8_t *)av_malloc(numBytes*sizeof(uint8_t));
  
  
  
  
  
      // Assign appropriate parts of buffer to image planes in pFrameRGB
  
      // Note that pFrameRGB is an AVFrame, but AVFrame is a superset
  
      // of AVPicture
  
      res = avpicture_fill((AVPicture *)pFrameRGB, buffer, AV_PIX_FMT_RGB24,
  
                      pCodecCtx->width, pCodecCtx->height);
  
      if (res&lt;0) {
  
          return;
  
      }
  
  
  
  
  
  
  
      // I've set this number randomly
  
      res = av_seek_frame(pFormatCtx, videoStream, 20.0, AVSEEK_FLAG_FRAME);
  
      if (res&lt;0) {
  
          return;
  
      }
  
  
  
  
  
  
  
      AVPacket packet;
  
      while(1) {
  
          av_read_frame(pFormatCtx, &amp;packet);
  
          if(packet.stream_index==videoStream) {
  
              int frameFinished;
  
              avcodec_decode_video2(pCodecCtx, pFrame, &amp;frameFinished, &amp;packet);
  
              if(frameFinished) {
  
                  SaveFrame(pFrameRGB, pCodecCtx->width,
  
                      pCodecCtx->height);
  
                  break;
  
              }
  
  
  
          }
  
      }
  
  
  
  
  
      avformat_close_input(&amp;pFormatCtx);
  
      return 0;
  
  }
  
  
  
  
  
  
  
  void SaveFrame(AVFrame *pFrame, int width, int height) {
  
    FILE *pFile;
  
    char szFilename[] = "frame.ppm";
  
    int  y;
  
  
  
    // Open file
  
    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);
  
  }

  I was following this tutorial http://dranger.com/ffmpeg/tutorial01.html http://dranger.com/ffmpeg/tutorial07.html . It says that it was updated in 2015, but there already are some warnings about deprecated code, for example here : pFormatCtx->streams[i]->codec.

  I got video duration (in microseconds), but I don’t understand what I should send to av_seek_frame. Can I somehow use frame number for both duration and seeking, instead of time ?

• mov : Save number of stsd elements after stream extradata allocation

  29 juin 2016, par Vittorio Giovara

  mov : Save number of stsd elements after stream extradata allocation
  Avoid freeing an unallocated array in mov_read_close() in case
  
  of a malloc failure.
  Signed-off-by : Vittorio Giovara <vittorio.giovara@gmail.com>
  

  • [DBH] libavformat/mov.c