What is the difference between Stream Copy and Re-Encode?

Lossless Stream Copy remuxes the original compressed video and audio packets directly without re-encoding (preserving 100% quality and running almost instantly), snapping to keyframes. Frame-Accurate Re-Encode decodes and re-encodes frames so cuts land on exact sub-second boundaries.

Does this upload my video to a server?

No. Video demuxing, trimming, and muxing run locally in your browser using Mediabunny and WebCodecs.

Video Trimmer & Cutter

Trim and cut MP4, MOV, and WebM video clips locally in your browser. Choose instant lossless keyframe stream-copy or frame-accurate WebCodecs re-encoding while keeping audio synchronized.

Drop an MP4, MOV, or WebM video to trim start and end points

Streaming BlobSource · Lossless stream-copy or frame-accurate re-encode · Preserves A/V sync

Zero server upload · Files never leave your device

TRIM RANGE & MODE

Start time (seconds)

End time (seconds)

Trimming mode

TRIMMED VIDEO PREVIEW & EXPORT

Load a video or click the sample clip button above to preview and export a trimmed segment.

Loading tool workspace…

Method and assumptions

Input video files (MP4, MOV, WebM) are read on demand via Mediabunny's BlobSource without loading the entire file into RAM at once. In Lossless Stream Copy mode, encoded video and audio packets within the selected [start, end] window are remuxed directly into the output container without decoding or re-encoding. When Frame-Accurate Re-Encode mode is selected (or when a stream-copy cut cannot align with container codec rules), frames are decoded and re-encoded via hardware-accelerated WebCodecs while preserving audio/video timestamp synchronization.

Common mistakes and edge cases

Lossless stream-copy cuts snap to the nearest preceding video keyframe (GOP boundary) so the first frame can decode cleanly. Choose Frame-Accurate Re-Encode when you need exact sub-second cuts between keyframes.

How to use

Drop an MP4, MOV, or WebM video into the workspace (or load the 3-second sample clip).
Enter your Start time and End time in seconds.
Choose Lossless Stream Copy (zero re-encoding) or Frame-Accurate Re-Encode.
Click Trim video, preview the trimmed clip in the video player, and click Download.

Example

Load the 3-second sample clip, set Start time to 0.5s and End time to 2.5s in Lossless Stream Copy mode, and click Trim video to export a 2.0-second clip with synchronized audio.

Frequently asked questions

What is the difference between Stream Copy and Re-Encode?: Lossless Stream Copy remuxes the original compressed video and audio packets directly without re-encoding (preserving 100% quality and running almost instantly), snapping to keyframes. Frame-Accurate Re-Encode decodes and re-encodes frames so cuts land on exact sub-second boundaries.
Does this upload my video to a server?: No. Video demuxing, trimming, and muxing run locally in your browser using Mediabunny and WebCodecs.

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This tool is provided for general informational and workflow purposes only. It does not constitute financial, investment, tax, or professional advice. All calculations run in your browser; no input data is transmitted or stored.