webReady: output.format must be mp4. Optimizes for web delivery via passthrough, faststart remux, or web encode. See Web Ready Video.
proxy: output.format must be mp4. Always re-encodes for timeline editing. See Edit Proxy.
extractAudio: output.format is the transcode fallback (mp3, aac, or wav). When the source audio is copy-compatible, the delivered file may use a different extension (for example .aac). See Extract Audio.
