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

[Mark Filipak]

On 08/06/2025 17.06, Jim DeLaHunt wrote:
> 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's exactly what I asked... where did you get that statement? Oh, [1]. I see.

I think that link should find a place in the FFmpeg documentation, eh?

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

https://ffmpeg.org/ffmpeg-codecs.html#flac-2 of course.

> 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.

I'm reading the so-called specification. It's vague. What is a 'block'? What is a 'frame'? It 
doesn't say, but it 'sounds' to me like transport, not encoding. Oh, well.

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

Thank you, Jim. You have heart.