depixelate effect/glitch, strobe. Shows how to control an effect vs time (start, duration, repetition).

bTimeEffect_DePixelate.hlsl

/*
bTimeEffect_DePixelate (square pixels) 
by butterw
control a video pixel shader effect vs time.  

tested in mpc-hc v1.9.3: 
- Opening the player by double clicking a video starts the clock
- Short effect/glitch repeats every 10 seconds by default (T).
- Note that Loading another video or Pause/Stop does not reset the clock !

The Effect here is Pixellation followed by De-Pixellation. On the first 2 runs it is preceded by a black screen.
Some version of the De-Pixellation effect was used when starting the game super mario world (SNES Mosaic effect).
The npixels values vs time could be further improved.

- at 5s, a fixed duration (td) non-repeating effect (blue screen strobe).
see Strobe.hlsl for a ready to use color frame insert (tstart, duration, repetition period).

*/

sampler s0: register(s0); 
float4 p0:  register(c0);
#define W  p0.x
#define H  p0.y
// #define Counter p0.z //float frame counter, starting at 0.
#define Clock p0.w //in s, starting at 0.
#define WH p0.xy

/* --- Pixelate  --- */ 
float4 Pixelate1(float2 tex, float npixels){
	/* rectangular pixels, npixels>1. (single pixel), Lower is more aggressive. */
	return tex2D(s0, floor(tex * npixels) / npixels); 
}

float4 Pixelate2(float2 tex, float npixels){
	/* square pixels version */ 
	float pixelSize = max(W, H) / npixels;
	return tex2D(s0, floor(tex * WH / pixelSize) * pixelSize/WH);
}

float4 Strobe(float4 inputColor) {
	/* returns the provided input color: placeholder for any effect/glitch */	
	return inputColor;
}	

	
float4 main(float2 tex: TEXCOORD0): COLOR {
	float4 c0 = tex2D(s0, tex);	// set c0 before calling functions that return tex2D (conditional compilation error !) 
	
	/*--- Pixelate Effect ---*/
	float T  = 10.; // T: Repetition period in seconds, no repetition if T=0.
	int nCycles = (T>0) ? int(Clock/T): 0; // Number of cycles calculation
	float t = Clock - nCycles*T; //Cycle time in seconds

	float4 ts = float4(1., 0.250, 0.350, 0.100); //start time and durations
	ts[1]+= ts[0]; ts[2]+= ts[1]; ts[3]+= ts[2]; //update times
	if (nCycles<=2 && t>=ts[0]-0.300 && t<ts[0]) 
		return Strobe(float4(1, 1, 1, 1)*16/255.); //black16 Screen
	if (t >= ts[0] && t < ts[1]) 
		return Pixelate2(tex, 215-1000.*(t-ts[0])); //fast pixel decrease
	if (t >= ts[1] && t < ts[2]) 
		return Pixelate2(tex, 15-20.*(t-ts[1])); 	
	if (t >= ts[2] && t < ts[3]) 		
		return Pixelate2(tex, 8); //constant low pixel			
	
	/*De-Pixelate Effect */
	ts[0] = ts[3]; //starts directly after Pixelate Effect	
	ts.yzw= float3(0.100, 0.350, 0.250); //set Durations
	ts[1]+= ts[0]; ts[2]+= ts[1]; ts[3]+= ts[2]; //update times
	if (t >= ts[0] && t < ts[1]) 
		return Pixelate2(tex, 8.);
	if (t >= ts[1] && t < ts[2]) 
		return Pixelate2(tex, 8+20.*(t-ts[1]));	//slow linear pixel increase
	if (t >= ts[2] && t < ts[3]) 
		return Pixelate2(tex, 15+1000.*(t-ts[2])); //fast pixel increase				
	//end of Effect	

	float tstart=5.; 
	float td=0.5;	//duration in s
	if (Clock>=tstart && Clock<tstart+td) return Strobe(float4(0, 0, 1, 0)); //Blue Screen, No repetition
	return c0;
}