proprietary codecs (H.264 / AAC) present for a Chrome UA
Check id codec-support
What an ordinary browser yields
H.264=true and AAC=true whenever a Chrome UA is presented — matching an official Chrome build's media stack.
What a detector infers
The check calls `canPlayType` on a video and audio element for H.264 ('avc1.42E01E') and AAC ('mp4a.40.2'), plus MP4/WebM/Ogg for context, and requires H.264 and AAC to both be supported. It only applies when the UA contains 'Chrome/' AND window.chrome is present (the IS_BLINK gate); otherwise N/A. The mechanism is build-configuration leakage: H.264 and AAC are licensed codecs compiled in for official Chrome builds, but stripped from many open-source Chromium builds and some headless/minimal images. A UA claiming desktop Chrome while the media stack cannot decode the formats every real Chrome can decode tells a detector the binary is not the browser it claims to be — and canPlayType is not something a UA string override reaches.
How to resolve it
Build or run a Chromium with proprietary_codecs enabled (ffmpeg_branding=Chrome) so the media stack matches the identity you present. Otherwise, do not advertise a Chrome UA on a codec-stripped build.
Nearby checks in Environment & locale
- IANA zone offset matches the JS clock offset (incl. across DST)
timezone-offset-coherenceThis is a two-source cross-check on the same fact. It takes the resolved IANA zone, formats the current instant through Intl.DateTimeFormat… - navigator.plugins is consistent with the PDF viewer
has-pluginsAn empty navigator.plugins is only meaningful when it contradicts something else, and this check is written to respect that. - navigator.pdfViewerEnabled is true
pdf-viewerA direct read of navigator.pdfViewerEnabled. It is N/A when the property is not exposed at all, passes when true, and is marked false… - mimeTypes are consistent with navigator.plugins
plugins-mimetypesThis walks navigator.mimeTypes, and for each entry reads .enabledPlugin and checks that the exact object is present in a Set built from… - Blink-only Web APIs present for a Chrome UA
blink-web-apisWhen the UA matches Chrome/\d+ and the page is a secure context, this probes four Blink-only surfaces: navigator.connection… - CSS feature support matches the engine (Blink for a Chrome UA)
css-engine-surfaceFor any UA containing 'Chrome/', this requires CSS.supports('-webkit-app-region', 'drag') to be true and the Gecko markers — MozAppearance… - every Intl constructor resolves the same locale
intl-locale-coherenceEvery Intl constructor — NumberFormat, DateTimeFormat, PluralRules, Collator — resolves its locale through the same underlying ICU data, so… - navigator.plugins is a real platform object (structured-clone probe)
plugins-structured-cloneThe structured-clone algorithm is implemented in C++ and interrogates objects about what they actually are, not what they claim.
Clearcote is a browser built for fingerprint coherence
It is a Chromium fork, maintained by the same people who wrote this reference. It ships as a compiled browser rather than as a stealth script injected into someone else's — which is a description of how it is built, and is not an argument about how it behaves on this check.
This audit takes no position on how Clearcote scores on Environment & locale checks, on this one, or anywhere else. It has no baseline corpus of other people's fingerprints to rank you against and no vendor scoreboard — nearly every check is self-referential, asking one browser the same question through two independent APIs and reporting whether both answers can be true at once. It runs identically on any browser, including ours. Run it on yours and read the result yourself.
See the other checks in Environment & locale — the family codec-support belongs to.