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• How to write AVFrame out as JPEG image

  10 novembre 2016, par John Allard

  I’m writing a program to extract images from a video stream. So far I have figured out how to seek to the correct frames, decode the video stream, and gather the relevant data into an AVFrame struct. I’m now trying to write the data out as a JPEG image, but my code isn’t working. The code I got is from here : https://gist.github.com/RLovelett/67856c5bfdf5739944ed

  int save_frame_as_jpeg(AVCodecContext *pCodecCtx, AVFrame *pFrame, int FrameNo) {
  
      AVCodec *jpegCodec = avcodec_find_encoder(AV_CODEC_ID_JPEG2000);
  
      if (!jpegCodec) {
  
          return -1;
  
      }
  
      AVCodecContext *jpegContext = avcodec_alloc_context3(jpegCodec);
  
      if (!jpegContext) {
  
          return -1;
  
      }
  
  
  
      jpegContext->pix_fmt = pCodecCtx->pix_fmt;
  
      jpegContext->height = pFrame->height;
  
      jpegContext->width = pFrame->width;
  
  
  
      if (avcodec_open2(jpegContext, jpegCodec, NULL) < 0) {
  
          return -1;
  
      }
  
      FILE *JPEGFile;
  
      char JPEGFName[256];
  
  
  
      AVPacket packet = {.data = NULL, .size = 0};
  
      av_init_packet(&packet);
  
      int gotFrame;
  
  
  
      if (avcodec_encode_video2(jpegContext, &packet, pFrame, &gotFrame) < 0) {
  
          return -1;
  
      }
  
  
  
      sprintf(JPEGFName, "dvr-%06d.jpg", FrameNo);
  
      JPEGFile = fopen(JPEGFName, "wb");
  
      fwrite(packet.data, 1, packet.size, JPEGFile);
  
      fclose(JPEGFile);
  
  
  
      av_free_packet(&packet);
  
      avcodec_close(jpegContext);
  
      return 0;
  
  }

  If I use that code, the first error I got was about the time_base on the AVCodecContext not being set. I set that to the timebase of my video decoding AVCodecContext struct. Now I’m getting another error

  [jpeg2000 @ 0x7fd6a4015200] dimensions not set
  
  [jpeg2000 @ 0x7fd6a307c400] dimensions not set
  
  [jpeg2000 @ 0x7fd6a5800000] dimensions not set
  
  [jpeg2000 @ 0x7fd6a307ca00] dimensions not set
  
  [jpeg2000 @ 0x7fd6a3092400] dimensions not set

  and the images still aren’t being written. From that Github Gist, one commenter claimed that the metadata isn’t being written to the JPEG image, but how should I write this metadata ? I did set the width and height of the encoding context, so I’m not sure why it claims the dimensions are not set.

• Downscale and padding with FFmpeg

  26 juin 2022, par nrofis

  I have an input video with a resolution of 3000x2160. I want to downscale it to 1920x1080 but keep the aspect ratio and center the original view by adding padding.

  


  I tried this command :

  


  ffmpeg -i input.mkv -c:v libx264 -vf scale=-1:1080,pad=1920:1080:'(ow-iw)/2':0 output.1080.mp4


  


  But I get an error :

  


  


  Padded dimensions cannot be smaller than input dimensions.

  


  


  Of course, since I want to add padding relatively to the output video size.

  


  How can I downscale and add padding to the output view ?

  


• avcodec/vc2enc : Simplify writing dirac golomb codes

  8 mars, par Andreas Rheinhardt

  avcodec/vc2enc : Simplify writing dirac golomb codes
  The earlier code used a loop to determine the number of bits used
  
  and called ff_log2() on a power of two (and it would be easy to
  
  keep track of the exponent of said power-of-two) ; neither GCC nor
  
  Clang optimized the loop away or avoided the ff_log2().
  
  This patch replaces the loop and the log2 with a single av_log2().
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
  

  • [DH] libavcodec/vc2enc.c