[GH-ISSUE #595] Downloaded FLAC files are upscaled lossy transcodes, not true lossless #1818

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opened 2026-03-13 19:32:59 +03:00 by kerem · 3 comments

kerem commented

2026-03-13 19:32:59 +03:00

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Originally created by @chuk-a on GitHub (Mar 3, 2026).
Original GitHub issue: https://github.com/afkarxyz/SpotiFLAC/issues/595

I've been downloading tracks using SpotiFLAC and testing the output files with VerifAI Audio — a spectral analysis tool that detects upscaled audio by measuring the high-frequency cutoff point.

Many of the downloaded FLAC files are not genuine lossless. They show hard frequency cutoffs consistent with lossy MP3 sources (128–320kbps) that were simply placed into a FLAC container. The file size is large but the audio quality is identical to a compressed MP3.

Originally created by @chuk-a on GitHub (Mar 3, 2026). Original GitHub issue: https://github.com/afkarxyz/SpotiFLAC/issues/595 I've been downloading tracks using SpotiFLAC and testing the output files with [VerifAI Audio](https://www.verifaiaudio.com/) — a spectral analysis tool that detects upscaled audio by measuring the high-frequency cutoff point. Many of the downloaded FLAC files are not genuine lossless. They show hard frequency cutoffs consistent with lossy MP3 sources (128–320kbps) that were simply placed into a FLAC container. The file size is large but the audio quality is identical to a compressed MP3.

kerem closed this issue

2026-03-13 19:33:04 +03:00

kerem commented

2026-03-13 19:33:10 +03:00

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@chuk-a commented on GitHub (Mar 3, 2026):

Gazebo - I Like Chopin Files labeled as FLAC should contain true lossless audio with full frequency extension to the Nyquist limit (~22.05 kHz for 44.1kHz sample rate). Many downloaded FLACs have hard frequency cutoffs at 16–20 kHz, indicating they are lossy transcodes (upscaled MP3s) packaged in a FLAC container. This results in unnecessarily large files with no quality benefit over the original MP3.
Verify the source quality from the upstream provider before saving as FLAC
If the source is lossy, either save it honestly as MP3/AAC, or add a warning to the user
Consider integrating a spectral analysis check to flag suspicious downloads

@chuk-a commented on GitHub (Mar 3, 2026): Gazebo - I Like Chopin Files labeled as FLAC should contain true lossless audio with full frequency extension to the Nyquist limit (~22.05 kHz for 44.1kHz sample rate). Many downloaded FLACs have hard frequency cutoffs at 16–20 kHz, indicating they are lossy transcodes (upscaled MP3s) packaged in a FLAC container. This results in unnecessarily large files with no quality benefit over the original MP3. Verify the source quality from the upstream provider before saving as FLAC If the source is lossy, either save it honestly as MP3/AAC, or add a warning to the user Consider integrating a spectral analysis check to flag suspicious downloads

kerem commented

2026-03-13 19:33:15 +03:00

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@chuk-a commented on GitHub (Mar 3, 2026):

please answer for my question.

@chuk-a commented on GitHub (Mar 3, 2026): please answer for my question.

kerem commented

2026-03-13 19:33:20 +03:00

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@pentium134-create commented on GitHub (Mar 3, 2026):

This site reports 326 kb aac as real lossless.
Just now i checked one song.

@pentium134-create commented on GitHub (Mar 3, 2026): This site reports 326 kb aac as real lossless. Just now i checked one song.