Do the clips need to match?

Not necessarily. If they share a codec and resolution the merge is an instant stream copy; if they differ, everything is re-encoded to one uniform H.264 file automatically.

How do I control the order?

Reorder the list with the arrows before merging — clips join top to bottom.

Memory is the limit: keep the combined size under roughly 1 GB on desktop, less on mobile.

Merge Videos — Join Clips Free, No Watermark

Join clips back to back in your browser: an instant stream-copy when they share a codec, an automatic re-encode when they don't.