What is actually inside the audio?
Codec history fingerprints the delivered audio for the block-boundary periodicity a lossy codec (Opus, MP3, AAC) leaves behind. It measures the stream as Speko received it — a fingerprint can originate anywhere in the path (the model, the vendor's transport, or our own gateway decode), so a spike flags a stream worth inspecting, not proof the vendor re-encoded.
Codec History
Periodicity strength at MDCT block boundaries (Opus 480, MP3 576, AAC 1024 / 2048). High strength = the delivered PCM carries a lossy-codec fingerprint somewhere in its path.
6 of 11 delivered streams show Opus-480 strength above 3.0 — a lossy-codec fingerprint worth inspecting, not proof of vendor-side re-encoding.