# Video Cutter & Merger

> Trim video, remove a section or join clips: lossless copy or frame-exact re-encode. Cuts a video to a start and end time, removes a section from the middle, or joins up to 5 clips in order. Copy mode is fast and lossless but cuts on keyframes; exact mode re-encodes (H.264/AAC) for frame-accurate cuts. Clips with identical settings are joined losslessly with the concat demuxer, others are normalised to a common size and frame rate first.

Part of usefulweb.site (https://usefulweb.site/). Results are deterministic calculations from the inputs and the listed assumptions; the API returns exactly what the web page shows.

## Use it
- Human interface: https://videocuttermerger.usefulweb.site/ (interactive tool at https://videocuttermerger.usefulweb.site/tool)
- JSON API: POST https://videocuttermerger.usefulweb.site/api/v1/calculate with a JSON object of inputs (schema: https://videocuttermerger.usefulweb.site/api/v1/tool)
- OpenAPI: https://videocuttermerger.usefulweb.site/openapi.json
- MCP (Streamable HTTP): https://videocuttermerger.usefulweb.site/mcp - tool `video_cutter_merger`

## Inputs
- mode (select): What to do
- file (file, required): Video file (clip 1) - MP4, MOV, MKV, WebM, AVI, MPEG-TS; max 250 MB and 20 minutes (in total when merging). Processed on our server in a private temporary folder that is deleted afterwards; the result can be downloaded for about 2 hours.
- file2 (file): Clip 2 (merge mode)
- file3 (file): Clip 3 (merge mode)
- file4 (file): Clip 4 (merge mode)
- file5 (file): Clip 5 (merge mode)
- start (text): Start time - Seconds, mm:ss or hh:mm:ss.mmm.
- end (text): End time - Empty = to the end.
- accuracy (select): Cut accuracy
- forceReencode (boolean): Merge: always normalise and re-encode (use if a lossless merge plays badly)

## Method
- Copy mode (-c copy) never re-encodes, so it is fast and lossless — but a video can only start on a keyframe. ffprobe lists the keyframes, and the tool reports where the cut really starts (the last keyframe at or before your start time). End points are exact to the frame.
- Exact mode trims with the trim/atrim filters and re-encodes with libx264 (veryfast, CRF 20) and AAC 160 kbit/s, so every cut lands on the requested frame.
- Remove a section: the parts before and after are kept and joined — by copying both parts and joining them with the concat demuxer (copy mode; the second part starts at a keyframe) or with the concat filter (exact mode).
- Merge: if all clips share codec, resolution, pixel format, frame rate and audio settings they are joined with the concat demuxer without re-encoding. Otherwise each clip is scaled and padded to the first clip's size (max 1080p), set to its frame rate, given silent audio if it has none, and joined with the concat filter.