Merge Videos

Join several clips into one video, with a straight cut or a half-second crossfade between them.

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What this tool does

Merge Videos hands your clips to ffmpeg on the OmniKitly processing service, which decodes every one of them, brings them to a common shape and writes a single file. Bringing them to a common shape is the part that does the work: each clip is scaled to the target size, padded to fill it, set to 30 frames per second and given 48 kHz stereo audio, because two streams cannot be concatenated until they agree on all of that.

Three settings decide the result. The output container is MP4, WebM, MOV or MKV — MP4 and MOV are written as H.264 with AAC audio, MKV the same without the streaming header, WebM as VP9 with Opus. When the clips differ in size you choose the target: match the first clip, match the largest, or force everything to 1080p or 720p. Between clips you get a straight cut or a 0.5 second crossfade, applied to the picture and the sound together and chained through the whole sequence, which makes the finished video half a second shorter at every join.

Anything smaller than the target is letterboxed rather than cropped or stretched — the clip is scaled until it fits inside the frame and the leftover space is filled with black, centred. A portrait phone clip dropped into a 1080p merge therefore keeps its whole picture with bars down each side, and target dimensions are rounded down to an even number of pixels because the encoders require it.

Two facts about the join matter more than anything in the settings panel. First, this is always a re-encode: there is no path that copies the streams untouched, so even joining two clips that already share a codec and a resolution costs one generation of quality, at a fixed constant-quality setting this tool does not expose. Second, every clip needs both a video track and an audio track. A file with no video is refused by name; a silent clip is worse, because the audio side of the filter graph has nothing to attach to and the whole job fails with a message about incompatible clips.

How to use it

  1. Add at least two clips. Fewer than two is refused — there is nothing to concatenate. Up to 50 files per job, each within the 200 MB upload ceiling.
  2. Check the order. Clips are joined in the order they sit in the queue, and the queue has no drag handles. To move a clip to the end, remove it and add it again.
  3. Choose the output container. MP4 for something that plays everywhere, WebM for the web, MOV for editing software, MKV when you do not care about either.
  4. Say what to do with clips of different sizes. Match the first clip, match the largest, or pin everything to 1080p or 720p. Whatever you pick, smaller clips gain black bars rather than losing picture.
  5. Pick a cut or a crossfade. A straight cut joins the clips exactly as they are. The crossfade dissolves picture and audio together over half a second and shortens the result by that much per join.

Processing & privacy

Secure server processing. This operation requires temporary server processing.

Common use cases

Recordings a camera split into chapters

Action cameras and dashcams break long takes into numbered files at the filesystem limit. Merging restores one continuous recording.

Clips shot on a phone at an event

Twenty short takes from a wedding or a talk become one file that can actually be sent, watched or archived.

Screen-recording takes

Record the tricky section again rather than in one go, then join the takes with a crossfade so the seam is not obvious.

An intro, the body and an outro

A title card and a closing card sit either side of the main footage without opening an editor to do it.

Footage from two cameras

A 4K camera and a phone can be pinned to a common 1080p target so the merged file has one consistent resolution.

Questions

Are my clips uploaded?
Yes. Video encoding needs a real encoder, so the clips travel over an encrypted connection to the processing service, ffmpeg joins them there, and the uploads, the merged file and the job record are deleted together when the retention window expires — six hours by default.
Do the clips have to match?
No. Different resolutions, aspect ratios, frame rates and codecs are all handled: each clip is scaled and padded to the target you chose, resampled to 30 fps, and its audio normalised to 48 kHz stereo before the join. The one thing that cannot vary is whether a track exists at all.
Why did my job fail when one clip has no sound?
Because the merge builds a combined audio stream from every input, and a clip without an audio track leaves that side of the graph with nothing to connect. There is no setting to substitute silence, so give the clip an audio track in an editor first, or leave it out.
Does merging lose quality?
Some, unavoidably. Unlike Merge PDF, which copies pages structurally, joining video means decoding and re-encoding every frame, so the output is one generation down from the source even when nothing else changes. Sources already heavily compressed show it most.
Can I reorder the clips after adding them?
Only by removing and re-adding. The queue keeps the order files arrived in, and multi-selecting in the file picker usually gives you the order your operating system sorted them by, which is not always the order you want.
How long can the clips be?
The first clip is measured before anything else and a file over three hours is refused as beyond the fair-use limit. Encoding also stops at ten minutes of processing, so a merge of several long, high-resolution clips can exceed that and fail even when each file is within the size ceiling.
What does the merged file come back as?
One file named merged, with the extension of the container you chose. Audio-only formats and GIF are refused here — converting the result is a separate job for Convert Video or Video to GIF.

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