Frequency reducer

I have a 12F683 pic recieving a stream of pulses from a device.

The mark space ratio is always 50% but the speed of the pulses varies from say 1hz upto 150hz.

Now what i want to do is time/measure the incoming pulses duration somehow and output on a different pin new pulses with the frequency reduced by say 30%

I thought about pulsin/pulsout but that won't work as you miss the start of the next pulse if you increase the length of the pulse you are sending out using that IIRC.

Any bright ideas? Or anyone done anything similiar before? Thanks