how do video scalers work
The scalar operation is 2D.
The normal architecture is performing horizontal and vertical interpolation seperately. For horizontal interpolation is just normal up-samlping method described in DSP book. The different are filter type(sinc, hamming window, etc..) and the taps of filter you choiced.
For veritical, the operation is the same. The different is you must keep some lines above and below the current line according the filter taps. This mean you must use ram as line buffer. For hw, the number of ram is the cost. It must be trade-off between cost and performace.
The filter can be non-adaptive or adaptive(changed acoording the context, like the edge appear...).
Regards,
Jarod