Video Cutter

Fast mode copies the video without re-encoding it, and a copy can only start at a keyframe. The nearest one before your start time is used. Exact mode re-encodes and starts exactly where you said.

Not in fast mode. The video data is copied, not re-compressed. Exact mode re-encodes the clip, which costs a little quality and a lot of time: in our test a four-second clip took under a second in fast mode and 15 seconds in exact mode.

Fast mode copies the piece straight out of an MP4 and never holds the file in memory, so several gigabytes is fine. Exact mode re-encodes and has to load the whole file, and a browser cannot read more than about 2 GB in one piece.

No. Everything happens inside your browser.

The video engine is about 10 MB compressed and is fetched once, then cached by your browser.

Both work, but they take different routes. An MP4 is cut straight out of the file in fast mode, with no download and no engine. Other formats are handed to the video engine, which your browser fetches the first time, and so is an MP4 written in fragments. The result is always saved as an MP4 named after your file with -cut on the end. A non-MP4 file over 2 GB cannot be read by the engine, so split it first.

Yes. In fast mode the audio from the same stretch is copied across with the picture, untouched. If an MP4 has more than one audio track, the fast route keeps the first one. Exact mode re-encodes both: the picture as H.264 and the sound as AAC at 160 kbps, which is why it is slower and loses a little quality. If a second or two of slack at the start is fine, fast mode gives you the sound exactly as it was.

Yes. Add them all, set the times once and press Start. They are cut one after another, each row shows its own progress, and you get a single zip at the end. The times are in seconds, with tenths allowed, so a cut at one minute fifteen is 75. If the end time is earlier than the start, nothing runs and the page says the range does not work.