How to Compress 4K Video with FFmpeg

4K video files can become huge very quickly. The best FFmpeg approach is usually quality-based compression with CRF, then optional downscaling if 4K resolution is not required.

For an interactive command builder, use the Compress Video tool.

Recommended 4K Compression Command

ffmpeg -i 4k-input.mp4 -c:v libx264 -crf 23 -preset medium -c:a aac -b:a 128k -pix_fmt yuv420p -movflags +faststart 4k-compressed.mp4

This creates a compatible H.264 MP4 with a practical balance of quality and file size.

Use this when:

• You want to keep the video at 4K.
• You need the result to play on common devices and browsers.
• You want quality-based compression instead of guessing a bitrate.

Choosing CRF for 4K

CRF	Result	Use when
18-20	High quality, larger file	Archiving, client delivery, premium output
22-24	Balanced	General uploads and web video
26-28	Smaller file, visible loss possible	Sharing, previews, storage savings

Start with 23. If the output is still too large, try 25 or 28. If details look soft, try 20.

Use H.265 for Smaller 4K Files

H.265 can reduce 4K file size more efficiently than H.264, but compatibility is less universal:

ffmpeg -i 4k-input.mp4 -c:v libx265 -crf 28 -preset medium -c:a aac -b:a 128k 4k-hevc.mp4

Use H.265 when the audience uses modern devices, or when the file is for storage rather than broad web playback.

Downscale 4K to 1080p

If viewers do not need 4K, downscaling gives the biggest file-size reduction:

ffmpeg -i 4k-input.mp4 -vf "scale=-2:1080" -c:v libx264 -crf 22 -preset medium -c:a aac -b:a 128k 1080p-output.mp4

The -2 keeps the width proportional and valid for H.264/H.265 encoders.

What the Options Mean

Option	Meaning
-c:v libx264	Encodes with H.264 for broad compatibility.
-c:v libx265	Encodes with H.265 for better compression on modern devices.
-crf	Controls quality and size. Lower means higher quality.
-preset medium	Balances encoding speed and compression efficiency.
-pix_fmt yuv420p	Improves playback compatibility.
-movflags +faststart	Helps web playback start sooner.

Common Problems

The compressed 4K file is still too large.
Try a higher CRF, use H.265, or downscale to 1080p.

The video takes too long to encode.
Use -preset fast or -preset veryfast. The file may be slightly larger.

The output does not play on older devices.
Use H.264 instead of H.265, keep .mp4, and include -pix_fmt yuv420p.

Related FFmpeg Pages

• Build a custom command with the Compress Video tool.
• See the recipe: Compress MP4 with FFmpeg.
• Learn the general guide: Compress video with FFmpeg.