RunLocalTools

Video Merger — Join Videos & Images Online for Free

Merge videos and images locally in your browser. Trim, reorder, add transitions and music, normalize audio, create chapters, choose output settings, and export without uploading your media.

What it does

Video Merger combines multiple video clips and still images into one finished video. You can reorder clips, trim their start and end points, change playback speed, rotate or flip footage, add transitions, control clip volume, add background audio, choose the output format and resolution, and export the result directly in your browser.

The tool includes an automatic join mode that checks whether compatible video streams can be joined without re-encoding. When that is not safe, it switches to a full local re-encode.

How it works

  1. Add videos, images, or both.
  2. The project is kept locally in your browser so a refresh can restore the work.
  3. Arrange and edit the clips in the desired order.
  4. Choose Auto, Fast Join, or Re-encode.
  5. Configure output size, aspect-ratio handling, frame rate, quality, audio and metadata options.
  6. Export the finished video locally.

Fast Join uses stream copying when the clips are compatible. Simple trims in Fast Join are keyframe-based; edits such as speed changes, rotation, flipping, reverse playback, images and transitions require re-encoding.

How to use it

Add media

Click the upload area or drag files into it. You can add multiple videos and images in one project.

Arrange clips

Drag clips into a different position, or use the up and down controls. You can also duplicate, reverse, or remove individual clips.

Trim and transform

Set the In and Out times for each clip. Change playback speed from 0.25× to 4×, adjust volume, rotate footage, or flip it horizontally or vertically.

Add transitions

Each clip can have a transition into the following clip. Available effects include cuts, fades, dissolves, wipes, slides, circle effects and pixelation where the local FFmpeg core supports the selected filter.

Add background audio

Add a local audio file as background music. Adjust its volume, optionally loop it to the video duration, and fade it out near the end.

Choose output settings

Use Auto when you want the tool to decide between fast joining and re-encoding. For re-encoding, choose the resolution, fit mode, frame rate, output format, quality and encoder speed.

Export

Start the local export and watch the progress, elapsed time and estimated remaining time. When complete, preview the result, download it, copy an equivalent FFmpeg command, or copy YouTube-style chapter timestamps.

FAQ

Can I merge videos with different resolutions?

Yes. Re-encode mode can combine clips with different dimensions, orientations and aspect ratios. Choose Contain to preserve the complete image with a background, Crop to Fill to fill the output frame, or Stretch if distortion is acceptable.

Can I merge videos and images together?

Yes. Images can be placed between video clips and given a duration. Adding images requires re-encoding.

Is the video uploaded to a server?

No. Video, image and audio processing happens locally in your browser. The tool does not send your media to a video-processing server.

What is Fast Join?

Fast Join uses FFmpeg stream copying when the clips have compatible streams. It avoids re-encoding, which can make compatible merges much faster and avoids another generation of video compression. Edited clips may need keyframe-based trimming or re-encoding depending on the requested changes.

Can I add background music?

Yes. Add an audio file from your device, adjust its volume, optionally loop it until the video ends, and optionally fade it out.

Can I create chapters?

For MP4 re-encoded exports, the tool can create chapter metadata using the source clip names. It can also copy the chapter timestamps as plain text for use elsewhere.

Privacy

Video Merger is local-first. Your videos, images and audio are processed in your browser and are not uploaded to a remote video-processing service.

The first export may download the pinned FFmpeg WebAssembly engine from the configured CDN. This network request downloads the processing engine only; your media is not sent with it. There are no remote video-import or remote-processing features in this tool.

Projects and source files are persisted locally by default so work survives a page refresh. Use Clear saved files & project to remove the saved project, source files and locally saved outputs for this tool.

Supported formats

Video input commonly includes MP4, M4V, MOV, WebM, MKV, AVI, WMV, FLV, MPEG/MPG, OGV, 3GP and transport-stream variants such as TS, MTS and M2TS, subject to the codecs available in the pinned FFmpeg core.

Image input includes common PNG, JPEG, WebP, GIF and BMP files.

Background audio accepts common browser/FFmpeg audio formats such as MP3, WAV, M4A, AAC, OGG, Opus and FLAC, subject to codec support.

Output formats are MP4 (H.264 + AAC) and WebM (VP9 + Opus).

Limitations

  • Re-encoding is CPU-intensive and can be slow in a browser, especially for long 1080p or higher-resolution projects.
  • Browser/WASM memory is limited. The tool estimates the input and output footprint and blocks projects that appear too large for the configured processing budget.
  • Fast Join requires compatible streams. Different codecs, frame rates, dimensions, pixel formats or audio streams can force re-encoding.
  • Fast Join trims are keyframe-based and are not guaranteed to be frame-accurate. Use Re-encode for precise trims.
  • Some camera and professional codecs may not be available in the pinned FFmpeg core. If a codec cannot be decoded, the export will report the failure instead of silently producing a bad file.
  • Some transitions depend on FFmpeg filter support in the loaded core.
  • WebM does not receive MP4 chapter metadata.
  • The sequence preview is a cut-only browser preview; it does not render every transition before export.
  • The tool does not provide cloud imports, remote processing, stock media, AI editing or server-side conversion.

For related local media workflows, see Audio Merger, Audio Track Extractor, GIF to MP4, and Video Frame Extractor.