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`wai inspect` reads envelopes; most files a toolchain meets are not envelopes, and the first question about one is what it is. `wai identify <file>` (operation media.inspect, extensions/media-identify.md) answers it for any file: - the formats the bytes fit, each with the offsets of the bytes that say so, how far its structure was followed and where and why that stopped; - a container's tracks as it states them: codec, size, channels, rate, protection; - the registered capabilities they map to, and what a format probe reads of them; - signatures found inside the file; - where no format is recognised, measures that still hold: how the byte values are spread, uniform windows, and the lags at which the bytes repeat. The verdict is identified, ambiguous, signature_only or unknown, and there is no confidence figure: a candidate's strength says what was checked. Nothing is decoded, no protected track is opened, and unknown stays unknown. Walks cover ISO media, Matroska, transport streams, Ogg, FLAC, RIFF, MPEG audio, ADTS, PNG, JPEG, GIF, IVF, YUV4MPEG2, FLV, AV1 OBU and Annex B streams, and HLS and DASH text; 35 more formats are known by their signature. Every walk is bounded, reads a file where its lengths lead (a large file is never held whole), and has been given hostile bytes; it builds for wasm32. The agent door has it as media_inspect, its results marked untrusted_content: a file's author chooses the strings in it. identify-conformance/ holds files written by real muxers and encoders from test patterns and tones, what an independent media prober reads of them (prober.json), and generated cases sitting on each rule's edge. identify_verify.py is a second implementation written from the text; it reads the extension's tables, gives every file its whole result, and holds ext/ to the prober's reading. tests/identify.rs holds the reference's tables to the extension's. Co-Authored-By: Claude Opus 5.5 <[email protected]>
21 lines
1.4 KiB
Markdown
21 lines
1.4 KiB
Markdown
# identify-conformance — media identification
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The corpus of [`extensions/media-identify.md`](../extensions/media-identify.md) §10.
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**Feature equivalence.** A conforming implementation, given a vector's file, gives the whole result
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`vectors.json` states for it: every candidate with its evidence, where its walk stopped and why, its
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facts, tracks and capabilities; what was embedded; and the measures. A vector with `repeat` is its
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file that many times over, for what happens past the head and past the scan (§3.2).
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- `ext/` — files written by real muxers and encoders, from test patterns and sine waves. The
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protected file uses an all-zero test key.
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- `gen/` — what `wai_identify_vectors gen` writes: generated cases and negative controls, each saying
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in `vectors.json` what it tests, many of them a change to a file of `ext/`.
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- `vectors.json` — every vector's file, SHA-256, origin and whole result.
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- `prober.json` — what an independent media prober reads of `ext/`: each file's format and streams.
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`identify_verify.py` holds the result to it wherever both state a value, so the reference and the
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second implementation agreeing is not all that is checked.
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- `identify_verify.py` — the second implementation, written from the extension.
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**Provenance.** `ext/` and `prober.json` are written by `tools/make_external.sh`, with open tools; it
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is not run in CI, because it needs them. `tools/oracle.py` writes `prober.json`.
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