Vamper reads the song, finds the parts it can wait in, and plays it so the music holds there until you say go. The join is on the beat and you shouldn't hear it. Add a few songs and jump between them with a click, or drop in a pack saved on another machine. Everything happens in your browser: the songs never leave your computer.
Fine-tune
Each part the song waits in is listed below. Switch a part off to let the song play through it, make it riff or loop, roll another riff, or hear it now. To wait in some other bars, drag across the waveform and press Add. Keys: Space pause and resume (or play), → go on, ← back, 1–9 jump to a part, D duck, M mute, A add the selected bars. A click on a part in the strip switches its hold on or off.
The small red ticks along the top of the waveform are where each four-bar phrase starts; a riff's jumps (the green arcs) always land in the same place of a phrase. A red mark under the waveform is a join that may have been heard, a pink one a join that cut a sung line.
Joins (debug)
Have fun with this tech: the same listening powers the Gondryator, which turns any song into a ride where the world keeps time with the music. How Vamper works. Talk about it on Discord, or buy Alex a coffee.