Using FFT as a channeliser
First, I suggest you take a look at the STFT.  

Let say you use $N$-point FFT, then you filterbank has $N/2$ filters (assuming real signal). Usually, you divide your signal into $K$ segments, each $N$ samples long (could be overlapping) and apply the FFT to each segment. Every time you apply the FFT you get a single sample for each filter. Therefore your filterbank has $N/2$ filters with $K$ samples.