Apple Silicon System on a Chip architecture
Rewind is designed for Apple Silicon (M1 and M2) chips. These chips have a System on a Chip (SoC) architecture which allows software (like Rewind) to offload processing to special purpose components of the chip (like machine learning inference), and NOT rely exclusively on the CPU. Only a portion of an Apple Silicon chip is considered the "CPU" (highlighted in the white box below):
Apple Silicon has multiple CPU cores
In addition to the special purpose components, each chip always has numerous CPU cores. The original M1 has 8 cores (4 performance 4 efficiency). The more recent M1 Ultra has 20 cores (16 performance and 4 efficiency). You can check how many cores you have by opening "System Information.app".
Typically, while recording, Rewind uses only 20 - 40% of a single core.
For M1 (8 cores), that translates to only 2.5 - 5% of all CPU capacity.
For M1 Ultra (20 cores), that translates to only 1 - 2% of all CPU capacity.
You can check how much CPU Rewind is using by opening "Activity Monitor" and searching for "Rewind":
Important: Activity Monitor shows you the percentage utilization of a single core. Your Mac could use 2000% of your CPU if you have a 20-core machine (like an M1 Ultra).