Dropping video frames

Question

my question is pretty simple, I think. And it's more about math than coding. I receive 15 frames per second from web-cam. But I have to drop some of these. For example, if client is requesting 8 fps - I do drop each second frame and it's ok. But how should I drop if 12 fps or 6 fps are requested?

I think there's some common algo for values distribution. Thanks a lot!

Answer 1

By dropping every 2nd frame for 8 fps, if you are having 15 fps, you are introducing an error.

This is a very simple algorithm, that would work in all cases :

#include <iostream>

double t = 0.0;

const double fps1 = 15.0;
const double fps2 = 12.0;

const double t1 = 1.0 / fps1;
const double t2 = 1.0 / fps2;

// true - drop the frame
// false - do NOT drop the frame
bool NextTick()
{
  t += t1;
  if ( t > t2 )
  {
    t -= t2;
    return false;
  }
  return true;
}

int main()
{
  for ( unsigned int i =0;i<20;++i)
  {
      if ( NextTick() )
      {
          std::cout<<"dropping the frame"<<std::endl;
      }
      else
      {
          std::cout<<"display the frame"<<std::endl;
      }
  }
}