Table of Contents

ffmpeg - Encoding - h265 - Constant Rate Factor (CRF)
- Example
- References

ffmpeg - Encoding - h265 - Constant Rate Factor (CRF)

Use this mode to retain good visual quality and do not care about the exact bitrate or filesize of the encoded file.

The mode works exactly the same as in x264, except that maximum value is always 51, even with 10-bit support, so please read the H.264 guide for more info.

ffmpeg -i "input.mkv" -map 0:v -map 0:a:m:language:eng? -map 0:s:m:language:eng? -map 0:d? -map 0:t? -c:v libx265 -crf 23 -c:a copy -threads 12 -bufsize 4M "out.mkv"

Example

ffmpeg -i input -c:v libx265 -crf 26 -preset fast -c:a aac -b:a 128k output.mp4

NOTE:

-crf: CRF affects the quality.
- The default is 28, and it should visually correspond to libx264 video at CRF 23, but result in about half the file size.
- CRF works just like in x264, so choose the highest value that provides an acceptable quality.

-preset fast: Choose a preset.
- The default is medium.
- The preset determines compression efficiency and therefore affects encoding speed.
- Valid presets are ultrafast, superfast, veryfast, faster, fast, medium, slow, slower, veryslow, and placebo.
  - Use the slowest preset you have patience for.
  - Ignore placebo as it provides insignificant returns for a significant increase in encoding time.

-tune: Choose a tune (optional).
- By default, this is disabled, and it is generally not required to set a tune option.
- x265 supports the following -tune options: psnr, ssim, grain, zerolatency, fastdecode.
  - They are explained in the H.264 guide.

References

https://trac.ffmpeg.org/wiki/Encode/H.264#crf