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What it does

Songs

  • Songs arrive in packages (.kmpkg). Each one carries its own queue numbers, titles, artists and analysis, and it goes in without a restart.
  • A language per song, so a catalog can say what Portuguese it has.
  • A 0–10 suitability rating for every file, with a breakdown.
  • The melody channel, where the machine can find it with confidence, and a stated reason where it cannot.
  • The first line or two of each song’s words, so a person can recognize the song. The machine skips the studio-name banner that many karaoke files open with.

Playing

  • Full-screen on a television, drawn by SDL3. On Linux it draws straight to DRM/KMS from a bare TTY, with no desktop installed.
  • Or on a television in another room, as a stream a browser or a playlist player opens. See Watching it in another room.
  • Words highlight in time, syllable by syllable, on the sequencer’s own clock.
  • Transpose and tempo per song, a guide melody that can be muted, and per-song defaults. A video, an MP3+G song and a song with recorded audio change key and tempo too. That needs more processing, so it starts off on Android and iOS, and the Playback pane turns it on.
  • A song ends when the rest of it is silent, and the next one starts. A quiet passage in the middle does not end a song. The Playback pane turns this off.
  • A lyric timing offset in milliseconds, adjustable mid-song, for the picture lag of a television. It moves the highlight only and never the audio, because the microphones are in that audio.
  • Wallpapers cycling with a crossfade, from a folder of stills or a zip of them.
  • A queue with singer names, shown over whatever is playing. Each queued song shows about how long until it starts.
  • An announcement before each queued song. For five seconds the whole screen shows the title, the artist and the singer’s name. A song with a long introduction plays under the card. The owner can change the length or turn it off.
  • A demo mode, off by default: after a minute of quiet the machine plays songs by itself until somebody queues one.

Two lines of the carol Angels From the Realms of Glory sung on the playing screen: each syllable fills in amber as it is sung, the next line waits below in gray, and when the first line ends the one after the next takes its row
Singing. Each syllable fills in time with the music, and the next line is already waiting.

Remotes

  • The machine serves a remote at its own address. Any phone on the network reaches it, with no app to install.
  • A standalone offline remote keeps its own copy of a machine’s catalog, and works with the machine switched off.
  • One admin password, which the machine shows on its own screen. Everything that reconfigures the machine needs it, and nothing a singer does needs it.
  • Songs play in the order asked, or the singers take turns. A guest asks for as many songs as they like. Out of the box each one goes to the end of the queue. Choose turns, and the machine keeps one song for each singer in the queue. The next one goes in when theirs starts.
  • Four levels below the owner: watch, ask, queue out of turn, and skip. Anybody in the room can ask for a song out of the box. You can lower that to watching only, or raise it. Three codes you choose raise one phone at a time. One queues out of turn and changes the key, one skips and plays now, and one opens the host’s tab.
  • A host runs a public night. At a bar or a hall, guests ask from their own phones and a host corrects from a tablet. See Running a public night.

Giving the machine pictures and instruments

  • KaraokeMachine Admin (km-admin) finds photographs the lyrics stay readable over. It also offers General MIDI banks from a table of sixty-three. It sends either to the machine, and it sends a package, a bank or a photograph of your own.
  • The machine downloads none of these itself, because it may have no internet and should not hold your accounts. km-admin keeps a copy of every download, to send to the machine later.
  • Pictures come from Openverse by default. Openverse needs no account, and its packs may travel on. Pixabay and Pexels need an API key of your own, and their terms forbid that.

Not supported, by decision

  • No scoring of singers.
  • No bare audio files, and no CD+G disc images — only the file pair.
  • No video wallpapers: a video song is not a video background.
  • No microphone processing in the app, because hardware mixes the microphones.
  • No Thai, Arabic or Indic words on the screen, and no right-to-left, though the machine draws Japanese and Chinese.

Each of these is a decision with a reason. To propose a change, start with docs/decisions/.