[zcorpan]

Add signatures for FLAC, HLS playlists, Matroska, AAC in ADTS, and MPEG-TS, and recognize more MP4 brands, matching Gecko. The Canon CR3 brand is excluded so CR3 files aren't sniffed as MP4.

Tests: web-platform-tests/wpt#64714.

Fixes #149.

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This is needed for opaque-response blocking (whatwg/fetch#1755), which blocks unlabeled responses to media requests unless they sniff as audio or video. Differences from Gecko's nsMediaSniffer.cpp: a crx major brand returns false (Gecko returns application/octet-stream, which ORB treats as a match), ADTS requires a frame length of at least 7, and avif isn't included as it's an image. ADTS with large frames can need more than 1445 bytes, see #218.

• At least two implementers are interested (and none opposed):
  • Gecko
  • …
• Tests are written and can be reviewed and commented upon at:
  • Update ORB tests for filtered fetch() responses and media sniffing web-platform-tests/wpt#64714 (fetch/orb/tentative/media.sub.html, fetch/orb/tentative/hls.html)
• Implementation bugs are filed:
  • Chromium: https://issues.chromium.org/issues/581932194
  • Gecko: already matches
  • WebKit: …
• MDN issue is filed: …
• The top of this comment includes a clear commit message to use.

(See WHATWG Working Mode: Changes for more details.)

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[annevk]

cc @padenot @jyavenard