What can I drop into each tab?
- Video to Lottie takes MP4, MOV or WebM and gives you a Lottie
.json. The video has to be something the browser can decode, which in practice means 8-bit 4:2:0 H.264.
- Shrink a Lottie takes a Lottie
.json that has image frames embedded in it, and returns a smaller .json plus a .json.gz where the browser supports it. A vector-only Lottie has no images to compress, and it will tell you so.
- Shrink a video takes MP4, MOV or WebM and returns MP4 on Safari and recent Chrome, WebM everywhere else. It says which before it starts.
Why is my Lottie bigger than the MP4 I made it from?
Because a video codec compresses across time — it stores what changed between frames — while a Lottie holding images stores each frame whole, then base64 adds roughly a third on top. A growth of several times over is normal and not a fault in the conversion. Lottie makes sense when a runtime requires it, not as a way to save weight.
Can I keep 25 fps and still get under 2 MB?
Often not. At full frame rate a ten second clip needs 250 separate images, and dividing 2 MB between them leaves so little per frame that the artefacts become obvious. Halving the frame rate doubles the budget for every remaining frame, which usually looks better than a full-rate file compressed to bits. The tool tests both against your actual footage rather than guessing.
What does "lossless" actually mean here?
When frames repeat exactly — a hold, a static section — the file stores one copy and points every repeat at it. Those frames come out bit-for-bit identical. That work happens first, and if it gets you under target on its own, the pixels are never re-compressed at all.
Why won't my MP4 load?
Almost always the codec. Browsers decode 8-bit 4:2:0 H.264; they don't handle HEVC reliably, 10-bit, 4:2:2, 4:4:4 or ProRes. The converter inspects the file header and names the exact problem, then gives you an ffmpeg command with your filename already in it.
Why does the video tab give me a WebM instead of an MP4?
A web page can only use the encoder the browser provides. Safari and recent Chrome can write MP4; other browsers only write WebM. The tool checks before it starts and tells you which you'll get, rather than renaming a WebM and hoping you don't notice.
Do my files get uploaded?
No. There is no server. Every file is read, decoded and re-encoded inside your browser tab. You can disconnect from the network after the page loads and everything still works.