How to Compress Video with FFmpeg

The most reliable way to reduce a video file size with FFmpeg is to re-encode the video with a quality target instead of guessing a fixed bitrate. For most MP4 files, that means using H.264 (libx264) with a CRF value.

If you want a form-based command builder, use the FFmpeg video compressor. If you just need the command, start here.

Recommended Command

ffmpeg -i input.mp4 -c:v libx264 -crf 23 -preset medium -c:a aac -b:a 128k -movflags +faststart output.mp4

This command creates a broadly compatible MP4 file, keeps quality reasonable, and usually makes the file much smaller than the original.

Use it when:

You want to upload a smaller video to a website or social platform.
You need an MP4 that plays in browsers, phones, and common video players.
You care more about visual quality than hitting an exact file size.

What the Options Mean

Option	Meaning
`-i input.mp4`	Sets the source video.
`-c:v libx264`	Encodes the video as H.264, the safest default for compatibility.
`-crf 23`	Sets the quality target. Lower values mean better quality and larger files.
`-preset medium`	Controls encoding speed versus compression efficiency.
`-c:a aac`	Encodes audio as AAC, which is widely supported in MP4.
`-b:a 128k`	Uses a practical audio bitrate for speech and general video.
`-movflags +faststart`	Moves MP4 metadata to the front so web playback can start sooner.

Choosing the Right CRF Value

CRF is the setting you will adjust most often.

CRF	Result	Best for
`18`	Very high quality, larger file	Archiving, editing, premium output
`20-23`	Good balance	Most web videos and uploads
`24-28`	Smaller file, visible loss possible	Previews, messaging, storage savings

Start with 23. If the file is still too large, try 25 or 28. If the quality drops too much, try 20.

Faster Compression

The preset changes how hard the encoder works. A slower preset can make a smaller file at the same CRF, but it takes longer.

ffmpeg -i input.mp4 -c:v libx264 -crf 23 -preset veryfast -c:a aac -b:a 128k output.mp4

Useful presets:

veryfast: good when you want quick results.
medium: balanced default.
slow: better compression if you can wait.

Avoid ultrafast unless speed matters more than file size. It often produces larger files.

Smaller Files with H.265

H.265/HEVC can produce smaller files than H.264 at similar visual quality, but compatibility is not as universal.

ffmpeg -i input.mp4 -c:v libx265 -crf 28 -preset medium -c:a aac -b:a 128k output.mp4

Use H.265 when:

Your audience uses modern devices.
You are storing video for yourself.
Smaller file size matters more than old-device compatibility.

For public websites and broad sharing, H.264 is still the safer default.

Compress to a Target Size

If you must hit a specific file size, use bitrate-based encoding. For example, this uses about 2 Mbps for video:

ffmpeg -i input.mp4 -c:v libx264 -b:v 2M -preset medium -c:a aac -b:a 128k output.mp4

CRF usually gives better quality for normal compression work. Target bitrate is useful when a platform has a strict upload limit.

Downscale While Compressing

Resolution has a huge effect on file size. If a 4K video does not need to stay 4K, downscale it:

ffmpeg -i input.mp4 -vf "scale=1920:-2" -c:v libx264 -crf 23 -preset medium -c:a aac -b:a 128k output.mp4

The -2 keeps the height proportional and makes sure the final dimension is valid for common encoders.

Common Mistakes

The output file is larger than the input.
The original may already be heavily compressed. Try a higher CRF, a slower preset, or downscale the resolution.

The video plays locally but not on a website.
Use H.264, AAC audio, .mp4, and -movflags +faststart.

The command says Unknown encoder 'libx264'.
Your FFmpeg build does not include x264. Install a full FFmpeg build or use an available encoder such as h264_videotoolbox on macOS. You can also check the FFmpeg error explainer.

Related FFmpeg Pages

Build a custom command with the Compress Video tool.
See the short recipe: Compress MP4 with FFmpeg.
Learn how to change video resolution with FFmpeg.