Merge MP4 or MOV video clips without re-encoding
Lossless in-browser clip concatenation. Joins videos with matching codecs, dimensions, and sample descriptions instantly without quality loss.
Select video clips to join
Lossless container concatenation. Joins matching clips end-to-end in milliseconds with zero quality loss and no watermark.
Related Video Tools
About this video joiner
Select two or more matching MP4 or MOV video clips, arrange them in your desired playback sequence, and click Merge Clips. The tool concatenates video and audio streams end-to-end without re-encoding, producing a single seamless video in seconds with zero loss in visual quality.
Merging video clips online typically involves uploading gigabytes of footage to third-party cloud servers and waiting through a slow transcode. That process degrades video sharpness and drains bandwidth. This tool performs lossless container concatenation directly in your browser. When clips share matching codecs and resolutions, their compressed packets are stitched end-to-end with recalibrated timecodes at local disk speeds.
Step by step
- 1Add video clipsSelect two or more MP4 or MOV video clips. The demuxer verifies codec and resolution compatibility.
- 2Arrange playback orderUse the move up and move down buttons to organize the clips into your preferred sequence.
- 3Validate container compatibilityThe engine validates that all clips share identical video codecs, frame dimensions, timescales, and sample descriptions (SPS/PPS).
- 4Export merged videoClick Merge Clips to join the timelines. The resulting video is packaged into a new MP4 container in seconds.
Strict compatibility validation for lossless merging
Lossless video merging without re-encoding is only possible when all clips share identical encoding parameters. Specifically, clips must have matching video codecs (e.g. H.264), identical pixel dimensions (e.g. 1920x1080), compatible timescales, and matching Sequence Parameter Sets (SPS) and Picture Parameter Sets (PPS) inside the sample description (stsd) atom. If you attempt to join clips with differing resolutions or profiles, the tool immediately halts and explains what differs rather than producing a corrupted file.
Timeline concatenation and timestamp recalibration
During merging, samples from the first clip are written with their original decode timestamps. For each subsequent clip, sample timestamps are offset by the cumulative duration of all preceding clips. Audio and video streams are synchronized independently, ensuring audio remains in perfect alignment with video throughout multi-clip playback.
Keyframe alignment at clip boundaries
To ensure seamless transition between clips, every subsequent clip must begin with a keyframe (I-frame / IDR frame). Because standalone video recordings naturally begin with an IDR keyframe, camera recordings and exported clips join cleanly without visual artifacts or frame stutter.
Audio track synchronization and channel mapping
Soundtracks require identical acoustic parameters across clips, including audio codec fourcc (typically mp4a for AAC), sample rate (such as 44,100 Hz or 48,000 Hz), and channel configurations (stereo vs mono). The engine validates each audio sample description before concatenation, aligning audio timestamps with the video track to prevent audio-video drift across long compilations.
Zero upload security guarantee
Every response from this site is served with a Content Security Policy whose connect-src directive is set to none. That is not a promise in marketing copy; it is an instruction to your browser, and the browser is the one enforcing it. While this page is open it cannot open a connection to anywhere — not to this site, not to anyone else — so there is no path by which your document could be uploaded, not by a bug, not by a future change, not by a script that should not be here. e2e/egress-proof.spec.ts asserts the served header and then tries to send data out by every route a page has and requires each attempt to be refused, and it runs on every build.
The second half of the guarantee is that the code has nowhere to send anything from. lib/tools/local-source-policy.test.ts reads every source file under lib/tools, workers, components and app on every test run and fails the build if any of them contains fetch, XMLHttpRequest, WebSocket, EventSource, sendBeacon or a peer connection, or even a remote address written down in a comment. A tool here cannot acquire an upload by accident, because the file that would have to contain one cannot be committed.
Client-side processing limits
Computations run directly on your own device using WebAssembly, Web Workers, and modern browser APIs including Web Crypto and TextDecoder. There are no server queues, no background telemetry, and no temporary cloud files created. Large operations remain responsive by offloading heavy parsing and conversion tasks to dedicated worker threads, ensuring the browser UI never freezes during intensive document and data processing tasks.
Questions people ask
- Does merging videos degrade quality?
- No. The video and audio packets from each clip are copied directly into the unified timeline without re-encoding, preserving 100% original visual quality.
- Can I merge videos with different resolutions or aspect ratios?
- Not without re-encoding. Lossless container concatenation requires all clips to share identical dimensions and codec parameters. Differing resolutions require a full transcode.
- How many clips can I join together?
- You can merge as many clips as desired with instant export times using zero-copy sample concatenation.
- Can I reorder clips before merging?
- Yes. Use the up and down arrows in the clip list to adjust the playback sequence before initiating the merge operation.
- Are my video clips uploaded anywhere?
- No. All files remain strictly on your local device, processed under connect-src none Content Security Policies with zero telemetry.