Two modes, one appJoin several videos side by side on a single canvas (one per LED wall), or cut a large video into several strips. You choose the mode at the top of the window.
One box per stripOn a UHD video, each LED strip has its own box, with the strip's real size (256×768, 512×768…), which you can drag and resize from any side or corner. With “keep proportion” on it never stretches; with it off, the box is free and the picture stretches to fill the strip. The strips are saved for next time.
One file per stripEach strip comes out as its own MP4, for independent players — for example in a run of strips where you can't pass cable between them — and, if you want, also a combined one with the strips side by side. It never overwrites a file that was already there.
Made for the playerH.264 output with the level limited to 5.1 and a fixed frame rate, so cheap Android boxes can decode it without a black screen. It shows beforehand what each strip will get, and ffmpeg is already included.