override fun onTracksChanged(tracks: Tracks) {
    tracks.groups.forEach { group ->
        for (i in 0 until group.length) {
            group.mediaTrackGroup.getFormat(i).metadata?.let { metadata ->
                for (j in 0 until metadata.length()) {
                    metadata.get(j).let {
                        if (it is TextInformationFrame) {
                            println("${it.id} ${it.values}") // TCON [<value>]
                        }

                        if (it is CommentFrame) {
                            println("${it.id} ${it.text}") // COMM <value>
                        }
                    }
                }
            }
        }
    }
}

override fun onMediaMetadataChanged(mediaMetadata: MediaMetadata) {
    println("genre: ${mediaMetadata.genre}") // null
    println("description: ${mediaMetadata.description}") // null
}