Cap trims Instant Mode CPU use by 40% and adds CLI API keys

Cap says Instant Mode in v0.5.8 uses 40% less CPU and 18% less peak memory with the same video quality.

The release also adds API keys for the Cap CLI, so you can record from CI, servers, and agents without a browser login.

Before recording, Cap now asks for confirmation if no microphone is selected or the selected microphone is unavailable. You can still choose to record without one.