Compressing Video with x264 and x265 in Avidemux

Camera and screen recordings are often many times larger than they need to be. Avidemux includes the x264 and x265 encoders, which can cut a file to a third of its size or less with no visible change. This guide covers the two ways to control size and the settings that matter.

Method 1: Constant Rate Factor (recommended)

CRF tells the encoder to keep a constant visual quality and use as many bits as that needs. Set Video Output to Mpeg4 AVC (x264), open Configure and choose Constant Rate Factor.

• x264: 18 is near transparent, 23 is a good default, 26 is small but still fine for viewing.
• x265: 22 to 28 covers the same range; x265 files come out 25 to 40 percent smaller than x264 at the same quality.

Method 2: Target size (two-pass)

If the output must fit a limit, such as 700 MB or an upload cap, pick Video Size (Two Pass) and enter the size in MB. Avidemux encodes the file twice; the first pass measures complexity and the second spends the bits where they are needed. Expect roughly double the encoding time.

Presets and tuning

The Preset option trades speed for compression efficiency. medium is the default; slow gives a few percent smaller files; veryslow is rarely worth it. Use Tune only when the content matches: film for camera footage, animation for cartoons, grain to preserve film grain.

Resolution and frame rate

Downscaling from 4K to 1080p with the swResize filter often saves more than any encoder setting, and 1080p is enough for most screens. Keep the frame rate as recorded unless the source was captured at an unusual rate.

Audio

Audio is small compared with video but still worth setting: AAC at 128 kbps for stereo speech and music, 192 kbps for high-quality music, or Copy if the source is already AAC.

Hardware encoders

On systems with NVIDIA, Intel or AMD GPUs, Avidemux lists NVENC, QSV or VA-API encoders. They are much faster but produce larger files at the same quality, so they are a better fit for quick previews than for archive copies.