Allow video wallpaper cropping

[andresjmorales]

As title says. Possibly: on editor canvas allow user to select a crame to work with in the editor, an when exporting the download, go through frame by frame and apply crop to each frame.

Note: I think most video wallpapers are only a few seconds on loop, not long videos. But I don't really even know how many people use video wallpapers, seems uncommon.

[andresjmorales]

After discussing with Claude:

Option A: FFmpeg in the browser via ffmpeg.wasm. This is the real answer. It's a WebAssembly build of FFmpeg that runs client-side. You'd extract the crop coordinates and scale factors from your existing layout math, translate them into FFmpeg filter commands (crop, scale, hstack/vstack), and let FFmpeg process the video. It handles encoding, frame-by-frame transforms, audio passthrough, all of it. The downside is ffmpeg.wasm is a ~30MB download and processing a long 4K video could take minutes and eat RAM. But it works and it's what serious browser-based video tools use.

Option B: Frame-by-frame canvas processing. Decode the video frame by frame, draw each frame onto your output canvas using the same stitching logic from generateOutput.ts, and encode the result using MediaRecorder or a WebCodecs-based encoder. This is more manual but avoids the ffmpeg.wasm dependency. It's slower and you lose fine control over encoding quality.

Option C: Don't process the video at all. Just export the crop/transform parameters and let the user apply them in their own video editor, or generate a script (FFmpeg command line) they can run locally. Way less work for you, but much worse UX.