-o/--output turns the equalizer into a pure PCM filter: "-" writes raw interleaved stereo s16le to stdout, any other value is a FIFO path (created if missing). Pipe outputs run at the input rate (no device clock, so no resampling) and are paced by the consumer via pipe backpressure; EPIPE ends the run quietly. The TUI and the gRPC control API work on all output modes, and the --no-tui API token is logged to stderr instead of stdout when stdout carries PCM.