libflac++-dev 1.3.3-1build1 (amd64 binary) in ubuntu focal

 FLAC stands for Free Lossless Audio Codec. Grossly oversimplified, FLAC is
 similar to MP3, but lossless. The FLAC project consists of:
 .
  * The stream format
  * libFLAC, which implements a reference encoder, stream decoder, and file
    decoder
  * flac, which is a command-line wrapper around libFLAC to encode and decode
    .flac files
  * Input plugins for various music players (Winamp, XMMS, and more in the
    works)
 .
 This package contains the development library libFLAC++.