Function write_flac 

pub(crate) fn write_flac(
    format: AudioFormat,
    samples: &[f32],
) -> Result<Vec<u8>, RecordingError>

Write interleaved samples as a lossless FLAC stream.

The samples quantize to 16 bits first, exactly as write_wav does, so the stream decodes back to the same samples the WAV would hold. It is the smaller of the two answers — a mix takes a third of the WAV’s bytes — which is why it is the format a caller gets when it names none.