The central processing unit performs general computing work in a device. During viewing it can handle application logic, some media processing and other system tasks, while specialised hardware may perform supported decoding. Processor performance is one factor among memory, storage, thermals, software and network delivery, so a CPU specification alone cannot predict every playback result.
A practical example
A device using software decoding for a demanding format may work its processor much harder than when supported decoding hardware handles the same type of task. The app can then feel less responsive even though the network delivers enough media data.
A common misunderstanding
Do not diagnose processor limitations only from a device's age or core count. Actual decoding support, encoding properties, software behaviour and system load affect the work the CPU must perform.
Related terms
Stable technical definition. Editorial approach