Merge Videos

How to use

1. Add every clip under Videos in one go, or drop them in a few at a time. Preview & download stays greyed out until two of them are in the list.
2. Drag a row by the grip on its right to move it. Whatever sits at the top plays first.
3. Click a clip's thumbnail to open it on the timeline, then pull the Clip start and Clip end handles in. The timeline is drawn from ten frames sampled across that clip, and the duration on the row updates while you drag.
4. Untick Audio on any clip you want silent. The box is already greyed out on clips that arrived without a sound track.
5. Pick the Output resolution and a Fit mode. Going above Source puts up a warning about upscaling, which is worth taking seriously on phone footage.
6. Set the transition on each gap row, choose MP4 or WebM, then press Preview & download. The finished video appears in a player above the Download button.

About this tool

Six takes of the same sentence, or two clips from the same afternoon. To merge videos into one file you drop them all on the Videos box, put the rows in the order they should play, and the tool renders a single new video out of the lot. The button underneath stays greyed out until there are two clips in the list, because one clip on its own is a trim job.

Clips almost never match each other. A phone held upright and a 1920×1080 screen capture are different shapes, and both have to end up inside one frame. Output resolution picks that frame. It opens on Source, which is the size of whichever clip carries the most pixels, with 1080p, 720p, 480p listed under it. Fit decides what happens to anything that doesn't match. Letterbox adds bars. Crop fills the frame and loses the edges. Stretch squashes the picture into shape.

Every gap between two rows carries its own transition picker. Left on None, the clips butt straight up against each other. Choose Crossfade, Fade to black, Fade to white, Blur dissolve, Slide, Wipe or Zoom and a seconds box appears beside it, starting at 0.5. That number is an overlap. The two clips play over the top of each other for that half second, which is why the finished video runs shorter than the two clips added together. Sound mostly follows the picture: Crossfade, Blur dissolve and Zoom mix the two tracks on an equal-power curve, and the two fades dip through silence before coming back.

Merging always re-encodes. Frames are pulled out of each clip, drawn into one canvas at the size you picked, and pushed back through the encoder at a flat 30 frames a second, so a 60 fps source gives up half its frames on the way through. The audio is rebuilt separately at 48 kHz stereo and laid under the finished picture. Press Preview & download, watch the bar, and the result saves as merged.mp4 or merged.webm depending on which format button you left selected. Cancel is live for the whole render.

Two clips, one crossfade, nineteen seconds

A 12-second screen capture at 1920×1080, then an 8-second clip shot upright on a phone at 720×1280. Source in the resolution menu reads 1920×1080, since the capture has more pixels than the phone clip. Left on Letterbox, the upright clip sits in the middle of that wide frame with bars down each side. Crop would fill the frame instead and take the top and bottom off the shot.

Set the join to Crossfade and change the 0.5 to 1. The clips now overlap for that second rather than running back to back, so merged.mp4 arrives at 19 seconds instead of 20, and the first clip's sound falls away over exactly the second the phone clip's comes up.

Good to know

• There is no lossless join. Every frame gets decoded, drawn onto a canvas and encoded again at a flat 30 fps, so a 60 fps clip comes back at half its frame rate and a long project takes real time to render.
• A transition can't run longer than half of the shorter clip beside it. Type 5 seconds between a 3-second clip and a 20-second one and you get 1.5.
• Slide and Wipe switch the audio at the midpoint instead of blending it. For sound that blends under a moving picture, Blur dissolve and Zoom both crossfade.
• The finished video is assembled in memory before it turns into a download, and the frames either side of every transition are held as bitmaps while they blend. That is the real ceiling on a phone.

Frequently asked questions