How to speed up or slow down a video on Windows 11?

Avidemux is an open-source video editor that allows you how to speed up or slow down a video to adjust the playback speed of video files on your computer.

Instructions: Open the software, click File → Open and select the target video, set both video and audio output to “Copy” for lossless processing, go to Video → Filters and select “Resample Frame Rate,” adjust the playback speed value, then click File → Save to export the modified video.

Its advantages include: open-source software, support for lossless video stream copying, and stable playback speed adjustment.

Its disadvantages include: the lack of a real-time preview window to check the speed effect, and the interface may be somewhat confusing for new users.

Notes:

• If you adjust the frame rate to significantly change the playback speed, the audio and video may become out of sync.
• Copy mode may not be compatible with all video formats; if saving fails, switch to a different encoding mode.
• Since you cannot preview the video, export a short test clip first to verify the playback speed.
• Extreme speed adjustments can cause audio distortion; you may need to edit the audio separately.

This allows you to conveniently adjust playback speed, whether you want how to speed up or slow down a video. It is suitable for users who need to modify video playback speed without loss of quality and, whenever possible, export the video without re-encoding.