How to Resize / Change Video Resolution in Avidemux

Q: How do I keep the aspect ratio?

Enable the aspect-ratio lock in the Resize filter before changing dimensions, so the picture is not distorted.

Q: How do I make vertical video for Shorts or Reels?

Resize to 1080x1920, or use the 'Fit to size' filter to place horizontal footage in a vertical frame with padding.

Q: Why is my resized video blurry?

Usually from upscaling a small source or aggressive compression. Resize down when possible and use a reasonable bitrate.

Resizing a video in Avidemux means changing its pixel dimensions — for example from 1920×1080 down to 1280×720 to reduce file size, or to 1080×1920 for vertical short-form video. This guide shows the step-by-step process with the Resize filter, aspect-ratio tips, and the quality caveats you should know first.

Step-by-step: resize a video

Open your video in Avidemux.
Go to Video > Filters in the menu.
Open the Transform category and double-click Resize.
Enter your target width and height, enable the aspect-ratio lock, and preview the result.
Choose an output format (Video Output must be an encoder, not Copy), then save the file.

Important: resizing requires re-encoding — you cannot resize in copy mode. The output will take longer to render than a simple cut, and the file is recompressed.

Common target sizes

Size	Resolution	Typical use
Full HD	1920×1080	YouTube, desktop playback
HD	1280×720	Smaller files, email / messaging
Vertical	1080×1920	Shorts, Reels, TikTok
4K UHD	3840×2160	High-resolution masters

Aspect ratio and “Fit to size”

Always keep the aspect ratio locked while resizing, or the picture will look stretched or squashed. If you need to place footage into a different frame (for example 4:3 footage inside a 16:9 frame), use the “Fit to size” filter in the same Transform category, which scales the video to fit a frame and pads the borders instead of distorting it.

Quality note: upscaling cannot add detail — enlarging 720p to 1080p only makes a bigger, softer file. Resize down from a high-quality master whenever possible for the best results.

Frequently asked questions

Will resizing reduce video quality?

Downscaling from a high-quality source keeps most visible quality but the file is recompressed during re-encoding. Upscaling cannot restore or add detail, so a 720p video will not become true 1080p.

How do I keep the aspect ratio?

In the Resize filter dialog, enable the aspect-ratio lock before changing either dimension. When you change one side, the other updates automatically and the picture is not distorted.

How do I make vertical video for Shorts or Reels?

Resize to 1080×1920, or use the “Fit to size” filter to place horizontal footage inside a 1080×1920 frame with padding instead of stretching it.

Why is my resized video blurry?

Blur usually comes from upscaling a small source or from aggressive compression settings. Resize down rather than up when possible, and use a reasonable encoder bitrate for the output.