Plex, Roon, and Navidrome trust the wrapper. Fake FLACs (lossy audio in lossless containers) play back as if they were genuinely lossless — and they're spreading.
FLAC is a lossless container. The audio inside it can be anything — including a 128 kbps MP3 source that someone transcoded to FLAC for storage. The wrapper is genuinely lossless; the audio is genuinely not. Plex, Roon, Navidrome, Subsonic, Jellyfin — every modern media server reads the container, sees "FLAC", lights up the lossless badge, and serves the file. The audiophile workflow trusts that badge. The audio doesn't deserve the trust.
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Rekordbox · Serato DJ · VirtualDJ (incl. Favorite Folders) on Windows 10+ and macOS (Apple Silicon + Intel).
Media servers don't audit because that's not what they're designed to do. They read tags, parse containers, and serve files — and that's the right scope for a media server. The audit step has to happen at the file system layer, and it has to happen at library scale. Music Library Doctor's FFT pipeline decodes each file and inspects the actual signal, regardless of container format. It runs on the file system directly, so Plex, Roon, Navidrome, and any other media server don't need plugins or integrations — clean up the files, the server rescans, the badges now mean what they say.
It sounds like its source. If the source was 128 kbps MP3, the playback sounds like a 128 kbps MP3 — the FLAC container can't add information that isn't there. The lossless badge is misleading you about what you're hearing.
Sometimes deception (torrent uploads passing off lossy as lossless). Sometimes well-meaning archiving (someone transcoding their MP3 collection to FLAC because they think it'll "preserve" it). The result is the same either way — disk space wasted, false lossless indicator.
Sometimes, on accurate playback gear. The high-frequency cliff at 16 kHz is audible in cymbals, air, and fast transients on a good system. But systematic library auditing is more reliable than per-track listening for a large collection.
Same principle — the FLAC contains what the source contained. A 320 kbps MP3 transcoded to FLAC is closer to lossless than a 128 kbps transcoded, but it's still lossy audio in a lossless container. FFT scoring would show a cliff at the higher frequency the 320 encoder allowed.
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