How to Configure libx265 Preset in FFmpeg

This article provides a straightforward guide on how to configure the preset parameter in FFmpeg’s libx265 encoder. You will learn what presets are, how they affect encoding speed and compression efficiency, and the exact commands needed to apply them to your video processing workflows.

Understanding libx265 Presets

In FFmpeg, the -preset parameter for the libx265 encoder determines the trade-off between encoding speed and compression efficiency. A slower preset provides better compression (smaller file size for the same quality), while a faster preset encodes the video quickly but results in a larger file size.

The available presets, from fastest to slowest, are:

• ultrafast
• superfast
• veryfast
• faster
• fast
• medium (the default preset)
• slow
• slower
• veryslow
• placebo (generally not recommended as it offers negligible quality gains for extremely long encoding times)

Command Syntax

To configure the preset, use the -preset option followed by the preset name in your FFmpeg command.

Example 1: Fast Encoding (Low CPU Usage)

If you need to encode a video quickly and do not mind a slightly larger file size, use a faster preset like veryfast:

ffmpeg -i input.mp4 -c:v libx265 -preset veryfast -crf 28 output.mp4

Example 2: High Compression (Optimized File Size)

For archival purposes where file size is a priority and you do not mind waiting longer for the encode to finish, use slow or veryslow:

ffmpeg -i input.mp4 -c:v libx265 -preset slow -crf 28 output.mp4

Recommended Best Practices

1. Pair with CRF: Always use the -preset parameter in conjunction with the -crf (Constant Rate Factor) parameter. For libx265, a CRF value between 20 and 28 is recommended. The preset will control how hard the encoder works to pack that target quality into the smallest possible file.
2. The Sweet Spot: For most general use cases, the slow preset offers the best balance between encoding time and compression efficiency.
3. Hardware Limitations: Avoid veryslow on older hardware, as HEVC (H.265) encoding is highly CPU-intensive.