UnderCap
Fit your supplementary video under the conference upload limit.
CMT, OpenReview and IEEE portals reject a supplementary file that's even slightly over the cap. Enter the exact MB limit and save a reviewer-friendly H.264 MP4 that fits — keeping resolution when it can, downscaling only when the cap is tight. Processed entirely in your browser; your unpublished video is never uploaded.
- 1 Drop your video
- 2 Set the size limit
- 3 Save the MP4 that fits
Enter the exact MB limit shown by your submission portal — these are common conference caps.
Safe for unpublished and double-blind work
Your video is processed in your browser's own memory — read, re-encoded with ffmpeg WebAssembly, and written back on your machine. There is no upload server in the loop, and no account to create — free or paid (you pay once and activate with a license key). Close the tab and the working data is gone.
Because the file never leaves your device, it stays appropriate for unpublished results and double-blind review. The output is an H.264 MP4 that targets a bitrate just under your chosen limit, so it plays anywhere reviewers open it.
Made for paper submission deadlines
When the portal rejects a 203 MB video against a 200 MB cap, you don't want to re-edit, re-export, re-upload, and hope again — least of all minutes before the deadline. UnderCap is built for that last-mile step: choose the cap, re-encode locally, and save an MP4 that fits.
It's not a general-purpose video compressor. It does one job — getting a supplementary video under a submission size limit — keeping the original resolution when the bitrate allows and downscaling only when a tight cap forces it. Built for the limits on the portals these venues use:
Pricing
Free: 3 full compressions, no sign-up — then $9 one-time for unlimited.
FAQ
Is my video uploaded anywhere?
No. The compressor runs as WebAssembly inside this page — your file is read, re-encoded, and written back entirely on your own computer. There is no server and no upload, so it is safe for double-blind review and unpublished work. Close the tab and the file is gone.
Which conferences and portals does it work for?
Any submission portal with a file-size cap, including CMT, OpenReview, and IEEE systems used by venues such as CVPR, ICCV, ECCV, NeurIPS, ICLR, CHI, SIGGRAPH, 3DV, and ISMAR. You enter the exact MB limit your portal requires.
Why not use a normal online video compressor?
Most online compressors require uploading your video. UnderCap is built for unpublished research videos, so compression happens locally in your browser — the file never leaves your device.
Does it change the video format?
Yes. It exports an H.264 MP4 with AAC audio for broad reviewer compatibility.
Can I use it for camera-ready and rebuttal materials?
Yes. It is designed for any submission step where the portal enforces a file-size cap, including camera-ready revisions and rebuttal materials.
What output format do I get?
An H.264 MP4 with AAC audio and faststart enabled — the most broadly compatible combination for reviewers, so the video plays wherever it is opened.
Will the result actually fit under the limit?
It targets a bitrate just under your cap, and for very tight caps it automatically reduces resolution to fit. If a cap is physically too small for the video's length, it tells you how short to trim instead of failing silently.
What about quality and resolution?
The original resolution is kept whenever the bitrate budget allows it; resolution is only lowered when it is the only way to fit. Encoding is single-pass for speed, so the final size lands close to — not exactly on — the target.
How large a file can it handle?
It works best for typical supplementary clips. Very long or high-resolution videos are slower and bounded by your browser's memory, since the encoder runs locally. If a file is large, the tool warns you before it starts.
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