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• How to create a circular countdown indicator overlayed into a video with ffmpeg ?

  18 novembre 2020, par Ben Holness

  I have a script that creates a video from multiple sources. At the start of the video there is a 5 second long pause where some information is displayed.

  


  I want to give a visual indicator of how long it is until the main video starts, with a circle in the top left corner. The circle would start completely transparent and slowly fill in grey round the circle as the video progresses. At 25% of the video, the top right quarter of the circle would be gray. At 50% the right half of the circle would be gray and so on.

  


  I am imagining something similar to this solution which is a progress bar, but I'm not sure if it's possible/how to make it a circular one.

  


• What is the difference between different fadein/fadeout curves in ffmpeg ?

  16 août 2018, par siods333333

  Here is the list of possible curves for afade and acrossfade filters from here https://ffmpeg.org/ffmpeg-filters.html#afade-1

  tri
  
      select triangular, linear slope (default) 
  
  
  
  qsin
  
      select quarter of sine wave 
  
  
  
  hsin
  
      select half of sine wave 
  
  
  
  esin
  
      select exponential sine wave 
  
  
  
  log
  
      select logarithmic 
  
  
  
  ipar
  
      select inverted parabola 
  
  
  
  qua
  
      select quadratic 
  
  
  
  cub
  
      select cubic 
  
  
  
  squ
  
      select square root 
  
  
  
  cbr
  
      select cubic root 
  
  
  
  par
  
      select parabola 
  
  
  
  exp
  
      select exponential 
  
  
  
  iqsin
  
      select inverted quarter of sine wave 
  
  
  
  ihsin
  
      select inverted half of sine wave 
  
  
  
  dese
  
      select double-exponential seat 
  
  
  
  desi
  
      select double-exponential sigmoid 

  Here is the code for them, from libavfilter/af_afade.c :

  switch (curve) {
  
  case QSIN:
  
      gain = sin(gain * M_PI / 2.0);
  
      break;
  
  case IQSIN:
  
      /* 0.6... = 2 / M_PI */
  
      gain = 0.6366197723675814 * asin(gain);
  
      break;
  
  case ESIN:
  
      gain = 1.0 - cos(M_PI / 4.0 * (CUBE(2.0*gain - 1) + 1));
  
      break;
  
  case HSIN:
  
      gain = (1.0 - cos(gain * M_PI)) / 2.0;
  
      break;
  
  case IHSIN:
  
      /* 0.3... = 1 / M_PI */
  
      gain = 0.3183098861837907 * acos(1 - 2 * gain);
  
      break;
  
  case EXP:
  
      /* -11.5... = 5*ln(0.1) */
  
      gain = exp(-11.512925464970227 * (1 - gain));
  
      break;
  
  case LOG:
  
      gain = av_clipd(1 + 0.2 * log10(gain), 0, 1.0);
  
      break;
  
  case PAR:
  
      gain = 1 - sqrt(1 - gain);
  
      break;
  
  case IPAR:
  
      gain = (1 - (1 - gain) * (1 - gain));
  
      break;
  
  case QUA:
  
      gain *= gain;
  
      break;
  
  case CUB:
  
      gain = CUBE(gain);
  
      break;
  
  case SQU:
  
      gain = sqrt(gain);
  
      break;
  
  case CBR:
  
      gain = cbrt(gain);
  
      break;
  
  case DESE:
  
      gain = gain <= 0.5 ? cbrt(2 * gain) / 2: 1 - cbrt(2 * (1 - gain)) / 2;
  
      break;
  
  case DESI:
  
      gain = gain <= 0.5 ? CUBE(2 * gain) / 2: 1 - CUBE(2 * (1 - gain)) / 2;
  
      break;
  
  }

  How do they look like ? How do they sound like ? Which one is recommended for fadein+fadeout and crossfade ? Personally I’m just trying to avoid audio clicks, maybe crossfade is a bit of an overkill here.

  Related link : http://manual.audacityteam.org/man/fade_and_crossfade.html . Not sure how audacity names translate into ffmpeg names though.

• What is the most efficient way to grab a specific frame from a video file by index ?

  4 février 2021, par Handelo

  So for some context - I'm creating a real-time data visualization tool in c# that needs to display video synced to other data. The playback needs to be stopped, resumed, scrubbed through and skipped through as smoothly as possible, similar to how it's done in video editing software, as well as have other data overlaid on top of it. To that end I do need the ability to get each frame by its index in a bitmap format. The video files are mostly MP4 encoded in x264, though support for other codecs is preferable.

  


  So far I've tried using both EMGU.CV and the Accord FFMPEG wrapper, but both solutions seem really slow at grabbing single frames - EMGU.CV's VideoCapture.SetCaptureProperty takes anywhere from half a second to 3 seconds to do so, and FFMPEG's VideoFileReader.ReadVideoFrame can take upwards of 10 (!) seconds.

  


  So what would be the most efficient solution here ? Is there another library I should try ?