Video Merger
Join multiple video clips into a single movie instantly.
Runs in your browser Your input never leaves your device.
Report a problem with this tool
About this tool
Choose two videos and the tool joins them end to end into one MP4: File 1 plays first, then File 2. It uses ffmpeg in WebAssembly, runs in your browser, and nothing is uploaded. Both clips are re-encoded to match the first: File 2 is scaled to fit File 1's frame size, with black bars if its shape differs, and both are set to 30 frames per second. If only one clip has sound, silence is added under the other so the audio stays in sync. Re-encoding is lossy and slow for long videos. Only two clips can be joined per run. The first run downloads the ffmpeg engine (about 25 MB), which can take from a few seconds to a minute on a slow connection; later runs on the same page reuse it.
How to use it
- Choose File 1, the clip that plays first.
- Choose File 2, the clip that follows.
- Press Process and wait for the progress bar.
- Preview and press Download.
What happens to each clip
- Frame size
- The result has the width and height of File 1. File 2 is scaled down or up to fit inside that frame without stretching, and any leftover area is filled with black.
- Frame rate
- Both clips are converted to 30 frames per second, so clips shot at 24, 25 or 60 fps play at the right speed but frames are dropped or repeated.
- Sound
- Audio is converted to stereo at 44.1 kHz. A clip with no sound gets silence for its length. If neither clip has sound, the result has no audio track.
Getting a clean join
- Trim the start and end of each clip first with the Video Trimmer, so the cut lands where you want it.
- Put the clip with the frame size you want as File 1. A landscape and a portrait clip in one video always leaves bars on one of them.
- For three or more clips, merge them in pairs and download each result before adding the next.
- Keep the clips short. Every frame is re-encoded on your device, so long or 4K videos take a long time.
Lossy re-encoding
Joining without re-encoding only works when both clips share the same codec, frame size and settings, which is rare for clips from different sources. This tool always re-encodes so that any two readable clips can be joined. The cost is time and a small loss of quality, so keep your original files.
Common problems
- Processing failed
- Both files must contain a video stream in a format ffmpeg can read. Convert the clip to MP4 with the Video Converter first, then merge again.
- The second clip has black bars
- The output uses File 1's frame size and File 2 is fitted inside it. Put the clip whose size you want first, or resize both to the same size with the Video Resizer before merging.
- I need to join more than two clips
- Merge two, then merge that result with the next clip.
- It is slow, or the tab freezes or runs out of memory
- ffmpeg runs on your device and holds both files in memory while it works. Use shorter or smaller files and close other heavy tabs.
Frequently asked questions
Can I merge a video with an audio file or music?
Not with this tool, which joins two videos one after the other. To put a music or voice file on a video, use Replace Video Audio.
Why does it not work in Safari?
This ffmpeg build needs cross-origin isolation and SharedArrayBuffer. If the browser does not provide them the tool shows a message. Use a current desktop Chrome, Edge or Firefox.
Are my videos uploaded?
No. The ffmpeg engine is downloaded to your browser and both clips are processed on your device.