How to Configure libx264 Preset in FFmpeg

This article explains how to use the preset parameter in the FFmpeg libx264 video encoder to balance encoding speed and file compression. You will learn the syntax for configuring presets, explore the available preset options from ultrafast to placebo, and see practical command-line examples to optimize your video encoding workflow.

Understanding the Preset Parameter

In FFmpeg, the -preset flag for the libx264 encoder determines the trade-off between encoding speed and compression efficiency. A faster preset will encode video quickly but result in a larger file size for a given quality level. Conversely, a slower preset takes more time and processing power to analyze the video, resulting in a smaller file size at the same quality level.

Available libx264 Presets

The libx264 encoder offers ten standard presets. Ordered from the fastest (lowest compression efficiency) to the slowest (highest compression efficiency), they are:

• ultrafast
• superfast
• veryfast
• faster
• fast
• medium (the default preset if none is specified)
• slow
• slower
• veryslow
• placebo (generally avoided, as it offers negligible compression gains over veryslow while drastically increasing encoding time)

FFmpeg Syntax and Examples

To configure the preset, add the -preset option followed by the preset name immediately after specifying the libx264 encoder with -c:v libx264.

Example 1: Fast Encoding for Live Streaming or Drafts

If you need to encode a video as quickly as possible and do not mind a slightly larger file size, use the veryfast or ultrafast preset:

ffmpeg -i input.mp4 -c:v libx264 -preset veryfast -crf 23 output.mp4

Example 2: Optimal Compression for Archiving (Recommended)

For archiving or uploading online where file size and quality are priorities, the slow or slower preset is recommended:

ffmpeg -i input.mp4 -c:v libx264 -preset slow -crf 22 output.mp4

Example 3: Balancing Speed and Quality

If you do not specify a preset, FFmpeg automatically applies the medium preset. However, you can declare it explicitly:

ffmpeg -i input.mp4 -c:v libx264 -preset medium -crf 23 output.mp4

Interaction with CRF (Constant Rate Factor)

When configuring presets, it is best practice to pair them with the Constant Rate Factor (-crf) parameter for quality control. The preset controls how hard the encoder works to compress the video, while the CRF controls the visual quality level (typically between 18 and 28, where lower means higher quality). Keeping the same CRF while changing the preset to a slower option will result in a smaller file size without sacrificing visual quality.