Join video clips into one file, in your browser
Phones and cameras save every recording as its own file. When you want one video out of several, say the parts of a talk, a few moments from a trip or the takes of a tutorial, you need to join them. This tool puts 2 to 10 clips one after another into a single MP4 or WebM file. It reads MP4, MOV, WebM and MKV videos and runs entirely in your browser tab, so the clips never leave your device.
The list shows each clip with a small picture, its size, frame rate, length and file size. Drag a clip by its handle or use the up and down arrows to change the order, and remove clips you do not need. The total length updates as you go.
How the merge works
Clips from different sources rarely share the same size, codec and sound settings, and a video file can only hold one of each per track. So the tool does not glue files together byte by byte. It decodes every frame of every clip with your browser's WebCodecs video decoder, draws it into one frame size and encodes it again. The new file is an MP4 with H.264 video when your browser can encode that, otherwise a WebM with VP9 video. The quality setting is the high preset of the open-source library mediabunny, which picks a bitrate from the frame size.
Sound gets the same care. The sound of each clip is decoded, mixed to stereo and converted to 48,000 samples per second, then encoded as AAC in an MP4 or Opus in a WebM. Each clip's sound is cut or filled with silence to exactly the clip's length, counted in single samples. Clips without sound get silence. That way the sound of the tenth clip still lines up with its picture, and a silent screen recording in the middle does not shift everything after it.
Different sizes and frame rates
- Output size: Largest clip uses the size of the clip with the most pixels, First clip the size of the clip at the top of the list. The three fixed sizes are a widescreen 1920 × 1080, a vertical 1080 × 1920 for phones and stories, and a square 1080 × 1080. Widths and heights are rounded to even numbers, which H.264 needs.
- Fit with bars: clips of another shape are shown whole, centered, with bars in the bar color around them.
- Fill and crop: every clip covers the whole frame; the parts that stick out on the sides or at the top and bottom are cut off.
- Frame rates: every frame keeps its own time in the new file. A 30 fps clip followed by a 60 fps clip plays both at normal speed, and no frames are invented.
- Sound: Keep writes one sound track for all clips, Leave out makes a silent video.
The small pictures in the list show each clip the way it will look in the chosen frame, so you see bars or cropping before you start.
A worked example
Say you have three clips: a 1920 × 1080 landscape clip of 0:40 with sound, a 1080 × 1920 phone clip of 0:25 with sound, and a 1280 × 720 screen recording of 1:10 without sound. With Largest clip and Fit with bars, the frame is 1920 × 1080, because 1,080 × 1,920 has the same number of pixels and the landscape clip comes first in the list. The phone clip is scaled to 608 × 1080 and gets black bars on the left and right. The screen recording is enlarged to fill the frame, since it has the same 16:9 shape. The merged video is 2:15 long, and the sound track has 70 seconds of silence at the end, where the screen recording plays. With 1080 × 1920 and Fill and crop instead, the phone clip fills the frame and the two landscape clips are cut to their middle part.
Browsers, iPhone and large files
Decoding and encoding video needs the WebCodecs VideoDecoder and VideoEncoder. According to MDN's compatibility data, these exist in Chrome and Edge 94 or newer, Firefox 130 or newer on computers and Safari 16.4 or newer, including iPhone and iPad, but not in Firefox for Android. Encoding the sound needs the AudioEncoder, which MDN lists for Safari only from version 26. On older iPhones and iPads the tool therefore makes a video without sound and tells you so.
The tool takes up to 10 clips and 2 GB in total, or 1 GB on iPhone and iPad. File sizes in the tool count 1 GB as 1,024 MB and 1 MB as 1,024 KB. The merged file is kept in memory until you download it, so a long video can still fail on a phone, and the tool warns on iPhone and iPad above 10 minutes. Cut long clips shorter with Trim Video first, and shrink the result with the video compressor if it is too big to send. Titles and other metadata of the clips are not copied into the new file.
How to merge videos
- 1Drop 2 to 10 videos on the box, or tap it to pick them from your files or photo library. You can add more clips later.
- 2Put the clips in order by dragging the handles or with the arrows, and remove any you do not want.
- 3Choose the output size, Fit with bars or Fill and crop, the bar color and whether to keep the sound.
- 4Press Merge videos, wait for the progress bar, check the result in the player and press Download video.
To change the shape of a single video, use the video resizer. To turn a sideways clip upright before merging, use Rotate Video.
Open-source software
Reading the clips and writing the new file is done by mediabunny, licensed under the Mozilla Public License 2.0 (MPL-2.0). The decoding and encoding itself is done by your browser.
Sources
- mediabunny: Media sinks: reading decoded frames and sound from a file
- mediabunny: Media sources: encoding frames from a canvas and sound samples into a new file
- MDN: VideoEncoder and VideoDecoder browser compatibility
- MDN: AudioEncoder browser compatibility (Safari 26)
- mediabunny license (MPL-2.0)
Related guides
- MP4 vs WebM vs MOV: Containers, Codecs and What to Export
- How Big Is a Video File? Size per Minute by Resolution
- Email Attachment Size Limits, and How to Get Under Them
Frequently asked questions
Are my videos uploaded?
No. Your browser reads the clips from your device, joins them and builds the new file in the same tab. Nothing is sent to a server.
Can I join clips of different sizes, like a phone video and a widescreen video?
Yes. Pick an output size, for example the largest clip or 1920 × 1080. With Fit with bars, every clip is shown whole and the free space is filled with the background color. With Fill and crop, every clip covers the whole frame and the parts that stick out are cut off.
What happens to clips without sound?
They get silence for their full length, so the sound of the clips after them still lines up with their picture. If none of the clips has sound, the merged file has no sound track.
Can I join clips with different frame rates?
Yes. Every frame keeps its own time in the new file, so a 30 fps clip and a 60 fps clip both play at their normal speed. Nothing is slowed down or sped up.
Which files work, and what do I get?
The tool reads MP4, MOV, WebM and MKV files that your browser can decode. The merged file is an MP4 with H.264 video and AAC sound when your browser can encode those, otherwise a WebM with VP9 video and Opus sound.
Is there a size limit?
Up to 10 clips and 2 GB in total, or 1 GB on iPhone and iPad (1 GB = 1,024 MB). The new file is kept in memory until you download it, so long videos can still fail on phones. Trim long clips first if that happens.
Why does merging take a while?
Every frame of every clip is decoded, drawn into the new frame size and encoded again. That is what lets clips of different sizes and formats end up in one file, but it takes about as long as the video plays or longer, depending on your device.