Mp3HD is a lossless audio codec delivering an archival format for storing digital audio, which has the unique benefit of being able to be played in standard mp3 on every existing mp3 decoder. Mp3HD is based on MPEG-1/MPEG-2 Layer 3, with file extension .mp3.
Key features:

Compression: An mp3HD file has 2 components. First is the standard mp3 file, which can be made using any mp3 bit rate. 192kbps is commonly used as it is virtually indistinguishable from a CD, and is a small file size. The additional data needed to create a lossless mp3HD file from the standard mp3 component is automatically calculated from the chosen mp3 bit rate. No special mp3HD settings are necessary.

Lossless format: Audio quality is equivalent to a CD (100% bit exact copy). The file size of an mp3HD song is approximately half of a CD track.

Future Proof: Mp3HD as it is bit exact to a CD can be considered an archival copy, which is future proof.

Compatibility: Mp3HD files are backward compatible and can be played on every mp3 devices

Multiple usage: Same as mp3, with more benefits: archival format, sound preservation and ultimate quality experience

Convenience: Use the same ID3 metadata as mp3 embedded track – album, artist, track, song, genre, etc.