A mezzanine is a high-quality intermediate copy of the source — the master from which all delivery renditions are encoded. It sits between the original camera/production master and the compressed files viewers actually receive. The mezzanine is deliberately kept at high bitrate and light compression (often an intra-frame codec like ProRes or a high-bitrate H.264/HEVC), trading storage cost for quality headroom.
The reason to keep a mezzanine rather than encode straight from the original is repeatability and quality: every rendition descends from one clean, normalized master, so re-encoding for a new codec, a new device, or a corrected ladder does not require going back to the raw production assets. It also decouples ingest/QC from the transcoding farm.
Because all downstream quality is capped by the mezzanine, QC focuses heavily on it: getting the mezzanine right — correct color, audio, captions, and no artifacts — is what protects every rendition encoded from it.
