Merge videos into one file, losslessly when you can
The Merge Videos tool joins 2 to 20 clips into a single video, in the order you choose. Drop your MP4, MOV, WebM or MKV files, drag them into order with a mouse or a finger, and press Merge videos. It is the quick way to stitch together the clips a phone splits long recordings into, combine a set of short takes for a story, or append an intro and an outro to a recording.
When every clip has the same format — the usual case for clips from one camera or one app — the tool joins them losslessly, copying their compressed packets one after another without re-encoding, so quality is untouched and the result is ready in seconds. When the clips differ in size, frame rate, codec or sound, it re-encodes them to one size and frame rate, letterboxing or cropping clips of another shape and filling silent clips with silence so the sound stays in sync. Everything runs on your device with WebCodecs and the Mediabunny library (MPL-2.0); nothing is uploaded.
How to use the Merge Videos
- Drop two or more videos onto the box, or click to choose them. You can add more later with Add videos.
- Put the clips in order: drag the handle on the left of each row, use the arrow buttons, or press Sort by name.
- Check the badge. Lossless join means the clips match and will be joined without re-encoding; Re-encode lists what differs.
- When re-encoding, choose the Output size, how to fit clips of another shape, the Frame rate, and an optional Crossfade.
- Press Merge videos, watch the result, and press Download merged video.
Merge Videos features
Lossless concatenation
Clips with identical codec settings are joined packet by packet, so the merged video is exactly as sharp as the originals and takes seconds to make.
Mixes any sizes and frame rates
Different resolutions are letterboxed or cropped to one frame size, and different frame rates are brought to one constant rate.
Silence where there is no sound
Clips without an audio track get silence of the right length, so the sound of later clips never drifts out of sync.
Optional crossfades
Blend each clip into the next over a quarter, half or full second, with an equal-power audio crossfade.
Reorder by drag, tap or name
Drag rows with a mouse or a finger, nudge them with arrow buttons, or sort by file name — handy for numbered phone clips.
Up to 20 clips, all private
Join up to twenty videos at a time; they are read from your device and never sent anywhere.
When can videos be merged without re-encoding?
A lossless join simply places the compressed frames of each clip after those of the previous clip and adjusts the timestamps. That only works when a player could decode every clip with the same settings, so the tool checks that all clips use the same video codec, the same frame size, the same encoder profile and stream headers, the same orientation, and — if they have sound — the same audio codec, sample rate and channel count. Clips that differ only in frame rate can still be joined losslessly, because each frame keeps its own timestamp.
Recordings from the same phone, camera, screen recorder or app normally pass these checks. Clips downloaded from different places, edited in different apps, or recorded in different modes (for example 4K and 1080p, or HDR and standard) usually do not, and are re-encoded instead. Ticking Always re-encode forces re-encoding when you want to change the size or frame rate anyway.
Letterbox or crop?
Clips with the same shape as the output are simply scaled, without bars or cropping.
| Option | What happens to a clip of another shape | Best for |
|---|---|---|
| Letterbox | Scaled to fit inside the frame; black bars fill the rest | Keeping every part of the picture, e.g. vertical clips in a landscape video |
| Crop to fill | Scaled to cover the frame; the edges that do not fit are cut off | A clean full-frame look when the subject is centred |
Tips for a smooth merge
- Trim the ends of each clip first with Trim Video — clips trimmed in fast mode keep their format, so they can still be joined losslessly.
- Mixing 25 and 30 fps footage? Choose the frame rate most of your clips use; the others are converted by repeating or dropping frames, as described on the Video Frame Rate Converter page.
- For a long recording that you want in pieces rather than one file, use Split Video.
- Crossfades shorten the merged video: each crossfade overlaps two clips, so a 0.5 s crossfade between three clips removes 1 s in total.
Merge Videos FAQ
How do I merge videos without losing quality?
Add clips recorded with the same settings. When the badge says “Lossless join”, the tool copies their compressed packets without re-encoding, so the merged file has exactly the original quality.
Can I combine videos with different resolutions?
Yes. The tool re-encodes them to the output size you choose and either letterboxes or crops clips of another shape, so every clip fills the same frame.
Why does the tool say it must re-encode my clips?
The note lists the reason — different sizes, codecs, encoder settings, orientation or audio formats, or a crossfade. Any of these stops a straight packet copy from playing correctly.
How many videos can I join at once?
Up to 20. The merged video is built in your browser’s memory, so very long or 4K clips need a device with plenty of free memory.
Is this video joiner free and private?
Yes. There is no watermark, sign-up or upload: the clips are processed on your device, and only the Mediabunny library is fetched from a public CDN.
What happens to clips without sound?
When clips are re-encoded, silence of the right length is added for clips that have no audio, so the sound of the following clips stays in sync with their pictures.