Simply pranayama can be taken as breathing exercise and meditation as mental or spiritual exercise.
Pranayama can be bahiranga and meditation can be called antaranga aspect of Ashtanga Yoga.
I may explain further that the last four Angas—Pratyahara (withdrawal), Dharana (concentration), Dhyana (meditation) and Samadhi—are regarded and referred to as the Antaranga aspect (inner yoga) of Patanjali’s Yoga, whereas the first four Angas Yama, Niyama, Asana and Pranayama—are generally referred to as the Bahiranga aspect of Yoga or as the outer Yoga
