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.
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