Layer, cut and mix videos into one MP4.
Put up to four videos on one frame, trim and split them on a timeline, give each layer its own volume, speed, voice pitch and reverb, then export a single MP4 at up to 4K. Everything runs in this tab.
A 3-second test voice goes through the same code the export uses. Each card then measures the result: how long it lasts, which note it sits on, and how long the sound rings on after the voice stops. Speed without a pitch change uses time-stretching (WSOLA); a pitch change without a speed change stretches first, then resamples.
Nothing in your source files is changed. Each row below says which file to read, from where to where, how fast, how it sounds and where it sits on the canvas. Export reads that list once per frame, 30 times a second, and draws the layers bottom to top. It updates as you edit above.
All eight work in the editor above. On a Mac, use Cmd for Ctrl.
An edited video is often too big to send, in the wrong format, or better as a loop.