No upload, 100% local, no account

Merge video files

Drop your video files, drag to reorder them, and download the merged MP4. Uses fast stream copy when possible, re-encodes when needed. Nothing is uploaded.

How Merge video files works

Merge several video files into a single clip, powered by ffmpeg compiled to WebAssembly. Choose fast copy mode to join compatible streams instantly without re-encoding, or switch to re-encode mode when source files use different codecs or resolutions.

Speed depends on your hardware: copy mode is near-instant but needs matching codec, resolution and frame rate, while re-encoding handles mismatched sources at the cost of time and a small quality trade-off. Merging many large files at once needs more RAM, so very long projects work best in smaller batches.

Frequently asked questions

Are my files uploaded to a server?

No. ffmpeg compiled to WebAssembly merges your clips in this browser tab, each file is read into memory on your own device and joined there (in Copy mode via the concat demuxer with no re-encode; in Re-encode mode via the concat filter into a single H.264/AAC stream), and the combined video is offered as a local download. Nothing reaches Sunasty or any third party. Open your browser's DevTools, go to the Network tab and watch: no request carries your videos.

What is the difference between copy mode and re-encode mode?

Copy mode stitches the video streams together without touching the codec data, it is fast and lossless but requires all clips to share the same codec, resolution, and frame rate. Re-encode mode transcodes everything into a single uniform stream, which handles mismatched sources but takes longer and involves a small quality trade-off.

How many files can I merge at once?

There is no hard limit enforced by the tool, but merging many large files at once requires more RAM. If your device runs low on memory the browser tab may slow down or crash. For very long projects, merging in smaller batches and then joining the results works reliably.

Does it work offline?

Yes, once the page and the ffmpeg engine have loaded at least once. The engine is sizeable and is fetched from the network on first use, but after that the full merge runs on your device with no internet connection required.

Is it free? Do I need an account?

It is completely free and requires no sign-up. There are no watermarks, no daily limits and no tracking cookies needed to use the tool.