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, and compares what the stream declares against what it actually contains. For a native S2S model the question is whether its output silently carries a fingerprint of the caller's input codec — an echo of your pipeline rather than its own clean stream.
Preliminary: a single native S2S model, measured across n=3 caller voices. A mismatch flags a stream worth inspecting, not proof of vendor-side re-encoding — a fingerprint can originate anywhere in the path.
Codec-History Contamination
Plain English: does the model's audio carry a fingerprint of the caller's audio codec, instead of its own? A mismatch means the model is echoing your input pipeline.
| Provider | Declared | Detected | Confidence | Match | Notes |
|---|---|---|---|---|---|
| native S2S model | pcm | pcm | 1.00 | match | PCM end-to-end via Speko WS |
What we found: the model declares and emits PCM end to end — declared and detected codecs match, so no input-codec echo. Rows where declared ≠ detected would mean the model is silently re-encoding or passing input frames through.