Exit codes

The CLI keeps these categories stable for shell and CI automation.

Code	Category	Meaning
0	Success	The requested operation completed.
2	Usage	Argparse syntax is invalid or a command group is incomplete.
3	Environment	FFmpeg or FFprobe is missing or cannot be started.
4	Validation	An input, typed option, path, or overwrite policy is invalid.
5	Processing	A valid job started but FFmpeg/FFprobe failed.
6	Partial success	A batch completed with both successes and failures.

Human diagnostics go to stderr for errors. JSON-producing commands write their document to stdout so automation can parse it independently.