Merge videos online, free
Combine clips into one video. Drop them in, put them in order, press Merge. Clips from the same camera join without re-encoding; mixed clips are fitted to one frame.
Two ways to join clips
Stream copy (concat demuxer). When every clip has the same codec, resolution and audio format, typically several clips from one phone, FFmpeg reads them one after another and writes the packets straight into a single file. No quality loss, and it takes seconds.
Re-encode (concat filter). When clips differ, say a vertical phone clip and a landscape screen recording, each is decoded, scaled into the first clip's frame with letterbox or pillarbox bars, resampled to 30 fps and 48 kHz stereo, then encoded as one H.264 (or VP8) stream. That takes as long as converting the full combined length.
Need the result smaller for sharing? That is SqueezeVideos' job.
Questions
Can I merge videos with different formats or sizes?
Yes. If the clips differ, each one is scaled to fit the first clip's frame (with black bars where the shape differs), set to 30 fps and re-encoded into one file.
Why was merging instant?
All clips shared the same codec, frame size and audio format, so they were joined with FFmpeg's concat demuxer, which copies packets without re-encoding.
Is there a limit on how many clips?
No fixed limit. Total memory is the constraint: keep the combined output under about 2 GB on a computer and a few hundred MB on a phone.
Are my videos uploaded?
No. Merging happens inside your browser tab.