WAV metadata preflight and RF64 refusal¶

The existing read_wav_metadata helper reads bounded RIFF/WAVE metadata for PCM or IEEE-float data. This contribution adds regression fixtures; it does not add RF64 support or change the runtime parser.

from openmed.multimodal.wav_metadata import WavMetadataError, read_wav_metadata

synthetic_rf64 = b"RF64\xff\xff\xff\xffWAVE"
try:
    read_wav_metadata(synthetic_rf64)
except WavMetadataError as error:
    assert error.category == "wav_signature_invalid"

Unsupported RF64 boundary¶

An RF64 envelope is rejected after reading its 12-byte header, before any ds64 chunk header or content is consumed. The current category is wav_signature_invalid. Here that means RF64 is outside the accepted RIFF/WAVE signature set; it does not assert that every RF64 file is malformed. Keep this observable category stable unless a deliberate API change is made later.

tests/fixtures/multimodal/rf64.py defines five deterministic, tiny cases: missing ds64, truncated ds64, valid-looking size metadata, duplicate ds64, and an oversized declared ds64 chunk. Each is at most 128 bytes, even where a length field describes gigabytes. They contain structural numeric headers only, no audio samples, descriptive metadata, patient information or real source names. These are refusal fixtures, not an RF64 conformance suite or decoding examples.

A source shorter than the required envelope produces wav_header_truncated. A header budget too small for the envelope produces wav_header_limit_exceeded before signature inspection. Tests pin those existing precedence rules as well. Short-read streams are supported; successful restoration preserves nonzero initial positions on seekable streams. Caller-owned streams are never closed.

Verification¶

uv run --frozen --extra dev pytest tests/unit/multimodal/test_wav_metadata.py -q

The added cases exercise byte input, real temporary files, short-read/nonseekable streams, read boundaries and seek restoration. An empty RIFF/WAVE file written by Python's standard-library wave writer remains a successful control. Existing RIFF/WAVE tests are retained, unmodified except for added imports and new tests. No external decoders, model weights, credentials or network calls are needed.