An ordinary metronome has one tempo. Real songs have sections. MetroBlocks describes a song as a list of blocks:
- lead-ins, for example two 4-bar count-ins with different click sounds;
- song blocks, each with a name, a number of bars, a tempo, a time signature, a click sound and an optional accent grouping for odd meters (for example 3+3+2).
A colour-coded timeline shows the structure and the length of the song, highlights the block that is playing, and starts playback from any block you click.
Playback uses the Web Audio API, scheduling every click ahead of time. The same song can be rendered offline with OfflineAudioContext and saved as a WAV click track. Songs are saved in the browser automatically and can be exported and imported as JSON.
It is a static web app with no server. The interface is in Polish.