Cutting and Trimming Video in Avidemux Without Re-encoding

The most common job in Avidemux is removing parts of a file: ads from a recording, dead air at the start of a screen capture or a long tail at the end of a camera clip. In Copy mode the program does not touch the picture data at all, so the cut finishes in a few seconds and the output looks exactly like the source.

Open the file and set Copy mode

Drag the file into the window. In the left panel, set both Video Output and Audio Output to Copy. Pick an Output Format that matches the source, for example MP4 Muxer for an MP4 file or Mkv Muxer for MKV.

Mark the section

1. Move the slider to the start of the section you want to remove and press A (or the [ key).
2. Move to the end of the section and press B (or ]).
3. Press Delete. The section disappears from the timeline and the total length updates.

Repeat this for every section you want gone. The selection between A and B is shown in colour on the timeline, so it is easy to see what will be removed.

Keyframes matter

In Copy mode a cut can only start on a keyframe (an I-frame), because the frames that follow depend on it. Use the keyframe buttons (Up and Down arrows) to jump to the nearest one. Avidemux shows a warning if marker A sits on a non-keyframe and offers to move it. The end marker B can sit on any frame.

If you need frame-exact cuts on files with long keyframe intervals, the alternative is to re-encode just that file with a video codec. Expect a longer save and a small quality change.

Keep only one part

To keep a single section instead of removing several, set A and B around the part you want and use Edit > Crop (keep selection). Everything outside the markers is dropped.

Save

Choose File > Save, give the output a new name and wait a moment. The progress window closes when the muxer has finished writing the file.