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• How to prescale a frame using ffmpeg and H.265

  20 juillet 2017, par akw

  I want to decode video frames with the H.265 coded (AV_CODEC_ID_HEVC)
  I use the following code :

  AVCodec *hevcCodec = avcodec_find_decoder(AV_CODEC_ID_HEVC);
  
  AVCodecContext *avctx  = avcodec_alloc_context3(hevcCodec);
  
  avcodec_open2(avctx, hevcCodec, 0);
  
  AVFrame *frame = av_frame_alloc();
  
  AVPacket pkt;
  
  av_init_packet(&pkt);
  
  pkt.data = myDataPtr;
  
  pkt.size = myDataSize;
  
  int got_frame = 0;
  
  avcodec_send_packet(avctx, &pkt);
  
  if (avcodec_receive_frame(avctx, frame) >=0 ) {
  
          got_frame = 1;
  
          ...
  
  }

  This works fine, I got my YUV frame and can process it further (like converting to RGB or scaling, etc.)
  However, I would like to somehow tell the ffmpeg library, to scale the AVFrame while decoding (a scale factor of a power of 2 would be sufficient).
  I don’t want to scale after converting to RGB or use swscale or anything. I have to decode a lot of frames and need a smaller resolution.

  Is it possible to give the AVCodecContext some hints to scale the frames ?
  (I tried setting avctx.width and avctx.height, but this did not help)

• ppc : Clarify and extend the cpuid check

  10 mai 2015, par Luca Barbato

  ppc : Clarify and extend the cpuid check
  Add POWER entries.
  

  • [DBH] libavutil/ppc/cpu.c

• Sub-pixel rendering with imagettftext()

  8 mars 2016, par user1661677

  I’m creating an image sequence, and encoding it to a video using PHP, GD library and ffmpeg. You’ll see I’m animating the two text layers inversely of each other, on the X axis. And with some simple operators $i/2 and $i/3, I’m trying to make their movement slower in the final animation.

  The problem I’m having is that when the video is rendered out, each layer’s text is only moving ever second, and third frame, respectively. This causes the animation to be a bit ’jerky’ and just not as smooth as Adobe After Effects with it’s ability to support sub-pixel rendering of elements.

  Is there any way to get imagettftext(), or some other method of drawing on images to support sub-pixel rendering ?

  Thank you.

  for ($i = 1; $i <= 125; $i++) {
  
  
  
      // Text on Image
  
      $front = imagecreatefromjpeg('front.jpg');
  
      $white = imagecolorallocate($front, 255, 255, 255);
  
      $text = 'some text';
  
      $text2 = 'some other text';
  
      $font = '/var/www/html/test/OpenSans-Bold.ttf';
  
  
  
      // Add text
  
      imagettftext($front, 60, 0, 1340-($i/2), 720, $white, $font, $text);
  
      imagettftext($front, 35, 0, 1240+($i/3), 800, $white, $font, $text2);
  
  
  
      // Write image to file
  
      imagejpeg($front, "images/".$i.".jpg", 100);
  
  }