[FFmpeg-user] Is FLAC lossless for compression_level > 0?

[Jim DeLaHunt]

On 2025-06-08 13:35, Mark Filipak wrote:

> Is FLAC (Free Lossless Audio Codec) lossless for compression_level > 0?

Yes, says the FLAC documentation[1]: it is "an audio format similar to 
MP3, but lossless, meaning that audio is compressed in FLAC without any 
loss in quality."


> That is possible of course -- trading compression for encoding time -- 
> but the documentation doesn't say.

/Which/ documentation?

FLAC's documentation of the FLAC stream format[2] says:

 1. File consists of metadata blocks and encoded audio data blocks.
 2. Audio data encoding has a lossless processing step of transforming
    (left, right) channel signals into (mid, side). The transformed
    channels can be encoded with smaller data size.
 3. Audio data is encoded as a difference (residual) between the actual
    signal and a model of the signal. The residual can be encoded in
    fewer bits than the original signal took to encode.
 4. Audio data block size is one factor in the tradeoff of resulting
    encoded size vs time required to encode.
 5. There are multiple models of the signal possible, and each model has
    some parameters. Choice of model and of parameters is another factor
    in the tradeoff of resulting encoded size vs time required to encode.

That should give you some idea of how values of compression_level > 0 an 
result in better compression while still remaining lossless.


[1] /FLAC website/, <https://xiph.org/flac/>
[2] /FLAC website/, *Format overview* 
<https://xiph.org/flac/documentation_format_overview.html>

Best regards,
     —Jim DeLaHunt