Structured error returned from Exmpeg calls.
reason is one of:
:invalid_request- bad arguments (missing path, malformed opts, non-numeric times).:io_error- libavformat could not open or read the input / output file.:decode_error- the decoder rejected a packet or could not drain a frame.:encode_error- the encoder rejected a frame or could not drain a packet.:unsupported- the build of FFmpeg this NIF is linked against has no muxer / demuxer / codec for the request.:runtime_error- internal NIF runtime fault (e.g. unexpected ffmpeg state).:nif_panic- the Rust side panicked; should never happen in practice.:native_error- fallback for unrecognised native error types.