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Glossary · concept

What is Lossless compression?

Lossless compression makes files smaller without discarding any data — the original is perfectly reconstructed when decoded. FLAC, ALAC (Apple Lossless), ZIP, and PNG are lossless formats. Lossless audio files are typically 3-5× larger than equivalent-quality MP3s. YouTube does not serve lossless audio.

Also called:lossless audio · flac · alac

Lossless compression works by finding patterns in the data and representing them more compactly. A 60-second silent audio track is mostly zeros, which compresses to almost nothing; a 60-second symphony has less redundancy and compresses less. The promise is reversibility: the original bytes come back exactly.

For audio, FLAC and ALAC are the common lossless codecs. They produce files about 2× the size of a 320 kbps MP3 for genuinely indistinguishable quality. Most music services that advertise "lossless" (Apple Music, Tidal, Qobuz) use FLAC or ALAC.

YouTube does not serve lossless audio. The highest-quality audio you can pull from a YouTube video is the original m4a (AAC) — lossy, but a direct copy with no further re-encoding. For lossless YouTube audio you'd need source files from outside YouTube's delivery pipeline.

Common questions

Is YouTube Premium audio lossless?
No. YouTube Premium increases the bitrate ceiling but still serves AAC (lossy). YouTube Music doesn't currently offer a lossless tier — Apple Music and Tidal are the consumer lossless options.
Can I convert MP3 to lossless?
No. The data thrown away by MP3 encoding is gone permanently. "Converting" an MP3 to FLAC produces a FLAC that perfectly reconstructs the MP3 — including all the MP3 artifacts. It does not recover lossless quality from a lossy source.

Related terms

Lossy compression

Lossy compression discards some data permanently to make files smaller.

M4A

M4A is an audio-only file format that wraps AAC-encoded audio in an MP4 container.

MP3

MP3 is the most widely supported audio format.

Codec

A codec is the algorithm that encodes (compresses) and decodes raw audio or video into a smaller stream.

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