How to Merge Videos Step by Step

Last reviewed: 2026-10-02

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To merge videos, open Video Merger, add two or more clips, order them, set any trims, transitions, frame shape and music, check the "Output:" line, press "Merge videos" and save with "Download merged video". It all runs in your browser - nothing is uploaded, and there is no sign-up or watermark.

Step 1 - open the tool

Go to Video Merger in a current Chrome, Edge or desktop Firefox, or Safari 16.4 or later. The tool fetches only its own code, cached after first use: about 0.7 MB on the first thumbnail or merge, about 1 MB more for AAC audio where the browser lacks an encoder (such as Safari before 26), and about 31 MB for compatibility mode. The developer tools Network tab shows no clip, music or merged video being uploaded. Before you start, see when a video merger is the right tool or how Video Merger compares with alternatives.

Step 2 - add your clips

Drag files onto "Drop video clips here", or press "Choose videos" and select several at once. MP4, MOV, M4V, WebM, MKV, AVI and other video types your browser lists are accepted. Each later batch joins the end of the strip. Audio-only files are rejected as clips - add them as music in Step 7.

Each card shows a thumbnail, file name, trimmed duration, resolution and a landscape, portrait or square hint. "Try two sample clips" loads two tiny built-in demos, one landscape and one portrait.

Step 3 - put the clips in order

Cards play back to back in the order shown. Drag a card by its thumbnail with the mouse or a finger, or use its "Move left" and "Move right" buttons. "Remove" takes a clip out. "Merge videos" needs at least two clips.

Step 4 - trim, rotate, mute and preview each clip

• "Trim", or a tap on the thumbnail, opens the clip as a strip of frames with a start handle and an end handle that move in 0.1 s steps; the card's duration updates as you drag.
• "Mute" silences the clip and "Unmute" restores it. Muted clips, like clips without audio, contribute silence, so sound stays in sync.
• "Rotate", in the view that "Trim" opens, turns the whole clip 90°, 180° or 270° clockwise; the preview, the strip of frames and the card thumbnail show it turned, and a merge with a rotated clip is re-encoded.
• "Preview" plays the trimmed range. If it reports that preview is not available in this browser, the clip will still be merged.

There is no per-clip volume level. To cut one recording into separate pieces, use the video splitter first.

Step 5 - choose transitions

Every gap has a selector: "No transition" (the default), "Crossfade", which dissolves picture and sound into the next clip, or "Fade through black", which fades out to black and silence, then fades the next clip in. To set every gap at once, choose an option under "Every gap" and press "Apply to all". "Transition length" - 0.5 s, 1 s or 1.5 s - applies to all transitions and shrinks when a clip is too short for it.

Each crossfade overlaps two clips and shortens the video by the transition length; fade through black keeps the length. Four 10-second clips (40 s) come out as:

Choice at all 3 gaps	Merged length
No transition or fade through black	40 s
Crossfade, 0.5 s	38.5 s
Crossfade, 1 s	37 s
Crossfade, 1.5 s	35.5 s
Crossfade, 1 s, each clip trimmed by 2 s	29 s

Step 6 - set frame shape, fit and quality

• "Frame shape": Original (the first clip's shape, after any "Rotate"), 16:9 (landscape), 9:16 (vertical), 1:1 (square) or 4:5 (portrait). For Original, put the clip with the shape you want first.
• "Fit": "Letterbox (show the whole clip)" fills spare space with black; "Crop to fill" scales the clip to cover the frame and trims the overflow from the centre.
• "Quality": Auto, 1080p or 720p, plus 4K on desktop browsers whose encoder reports 4K support. The number is the short side, so 1080p at 9:16 is 1080 x 1920. Auto uses the first clip's resolution for Original, otherwise the largest clip's short side - never above 1080 either way.

Portrait phone clips with a rotation flag come out upright.

Step 7 - add background music (optional)

Press "Add music" and pick any audio file the browser can decode, such as MP3, M4A/AAC, WAV, OGG, Opus or FLAC. It is mixed under the clip audio:

• "Music volume": 0 to 100 %, starting at 80 %.
• "Clip audio while music plays": Keep (100 %), Lower (25 %, the default) or Mute (0 %), for all clips at once.
• "Loop music if it is shorter than the video": on by default.
• "Fade music out at the end": on by default, a 2-second fade.

"Remove music" takes it out.

Step 8 - check the "Output:" line

The "Output:" line names the format before you merge, for example "Output: MP4 (H.264 + AAC)" or "Output: WebM (VP9 + Opus) - this browser cannot encode H.264". "Format" sets the file type: "Auto (best for this browser)" picks MP4 (H.264) when the browser can encode it, otherwise WebM, and you can instead choose "MP4 (H.264)", "WebM (VP9)" or "WebM (AV1)" - a choice this browser cannot encode is greyed out, and compatibility mode always makes MP4 (H.264). Video Merger also warns before merging when the estimated output is large: over about 1.5 GB with browser encode, or about 500 MB of total input in compatibility mode on a desktop, less on phones.

Step 9 - press "Merge videos" and keep the tab open

Pressing "Merge videos" brings up a progress bar, percent, time-left estimate, current step, engine badge and "Cancel" button; the tool asks the browser to keep the screen awake where Screen Wake Lock is supported and reminds you to keep the tab open. The engine is chosen automatically:

Badge	Runs when	Speed	Output
"Lossless join - no re-encode"	Matching clips, no edits	Typically seconds	No quality loss; MP4 for H.264 or HEVC, WebM for VP8, VP9 or AV1
"Encoding in your browser (WebCodecs)"	Default for other merges	In tests on a recent laptop, less than the video's length; slower on older or low-power devices	MP4 (H.264), else WebM; up to 60 fps
"Compatibility mode (slower)"	No WebCodecs, a codec WebCodecs cannot decode, a container such as AVI, or a WebCodecs encoder failure	Slower - single-thread FFmpeg in WebAssembly; in some browsers many times the video's length	MP4 (H.264 + AAC); max 720p short side, max 30 fps

Step 10 - download, then "Merge again" or "Start over"

A playable preview appears with "Download merged video", which saves a file such as merged-3-clips.mp4 (or .webm), plus a summary of clip count, duration, resolution, size and engine. "Merge again" keeps clips and settings for another run, such as a 9:16 version after a 16:9 one. "Start over" clears everything - download first, because nothing is kept after it or after the tab closes.

Troubleshooting

The badge says "Compatibility mode (slower)"

A trigger from the Step 9 table applies - for example, HEVC clips in Chrome without a hardware HEVC decoder, or any merge in Firefox on Android, which has no WebCodecs. If speed matters, press "Cancel" and try another supported browser, or convert the affected clips first with the in-browser HD video converter.

A clip cannot be read or decoded

The red panel names the clip and the reason, such as an unsupported codec in this browser or an unreadable file. Check that the file plays elsewhere and copied completely; DRM-protected video cannot be merged. Otherwise "Remove" that card or try another browser.

The merge is slow

Speed depends on device and browser (see the Step 9 table). Trim unneeded footage and close heavy apps.

The browser runs out of memory

Device memory, not a server cap, is the limit behind the Step 8 warning. If the red panel reports not enough memory, close other tabs, trim or drop clips, choose 720p (under half the pixels of 1080p), or use a computer, not a phone.

The merge pauses or stops on a phone

On phones, keep the tab open and in front until "Download merged video" appears: closing it stops the merge, and some browsers pause hidden tabs, which Video Merger warns about.

The file is WebM instead of MP4

Browser encode tries H.264 in MP4 first, then VP9, AV1 and VP8 in WebM, and lossless joins can also give WebM (see Step 9). For MP4, set "Format" to "MP4 (H.264)" before merging; if that choice is greyed out, try another supported browser or convert the result with the in-browser HD video converter.

Frequently asked questions

When does a merge keep the original quality?

Only when the lossless join runs, because it copies the original data. That needs every clip to share the same video codec, codec settings, resolution, rotation flag and audio format (or no clip to have audio), plus no trim, mute, rotation, transition or music, "Frame shape" on Original and "Quality" on Auto. Anything else is re-encoded - lossy, at a high quality setting, but not bit-identical.

Can I add titles, text or slow motion?

No - there is no text, titles, stickers, captions, filters, effects, keyframes, voice-over or speed change. For text, captions, effects or keyframes, press "Edit in Video Editor": it opens these clips, with their trims, rotations, mute and music, in the multi-track video editor in a new tab.

Why do my HDR clips look different after merging?

HDR and 10-bit clips are converted to a standard 8-bit (SDR) output, so colours can look different from the original HDR playback. If colour matters, check the Step 10 preview before downloading.

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Last updated: Oct 5, 2026