Video Merge joins several videos end to end into one file: a phone-recorded vlog shot in parts, dash-cam clips written one minute at a time, or course chapters recorded separately. It is the “Merge” tab of the audio/video workbench. It probes the container, video codec, resolution and audio codec of every selected file, and when all four match it stream-copies through concat — no decode, no re-encode, done in seconds, zero quality loss. If any one of them differs it switches to re-encoding automatically.

Re-encoding takes the width and height of the first video as the target; other clips are scaled proportionally and centred with black bars, the frame rate is unified at 30 fps and audio at 48 kHz stereo, and the output is H.264 CRF 23 + AAC 128 kbps in an MP4 container. Clips without sound get a silent track of the same length so that picture and audio stay in sync after the join.

1. 01Add at least two videos— drag them all into the workbench and switch to the “Merge” tab. Every video is selected by default and ordered as added, and each row shows its duration and size.
2. 02Reorder and drop clips— use the up/down arrows at the right of each row and clear the checkbox on clips you do not want.
3. 03Read the mode hint— the panel states either “matching formats: lossless stream copy” or “mixed formats: will be re-encoded to MP4 (using the first video's resolution …)”; the button stays disabled while a file is still being probed.
4. 04Merge and download— click “Start merging”, then download merged_3_videos.mp4 when it finishes (under stream copy the extension follows the source).

Strict stream-copy test

— a different container extension, video codec, width, height or audio codec each force a re-encode; two MP4s at 1080p and 4K also re-encode.

Hidden risks of stream copy

— files whose encoding parameters (profile, frame rate, timebase) differ can still pass the test, and the join may stutter or jump in timestamps; re-encoding is safer when that happens.

Re-encoding time

— it runs at about one fifth to one tenth of native speed in the browser; AV1 sources cannot be re-encoded.

How frames are unified

— only black bars are added, never cropping, so a portrait clip in a landscape project becomes wide bars on both sides.

What it does not do

— no transitions (the join is a hard cut), no silence or black frames inserted between clips, and no audio-only merging (use “Audio trim and merge”).

Every clip is read and joined locally in the browser by ffmpeg.wasm and nothing is uploaded. On first use the engine, about 31 MB, is downloaded from a CDN (the site asset domain or jsDelivr); that request contains no video content.