How do diodes and capacitors reduce Crossover distortion?
Cross over distortion of a class B amplifier: -



The top half of the waveform comes from TR1 conducting and the bottom half from TR2 conducting. At some point a class B amplifier changes from using the top transistor to the bottom transistor. When this happens there is insufficient voltage across base/emitter to activate either transistor hence there is a dead zone: -



The diodes turn a class B design into a class AB. Now, neither transistor is fully off therefore the dead zone is no more.

The capacitors are incidental - they allow the input signal to couple to both bases without the new biasing arrangement being affected.