====== 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 [[https://trac.ffmpeg.org/wiki/Encode/H.264#crf|H.264]] guide for more info. 

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<code bash>
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"
</code>

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===== Example =====

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

<WRAP info>
**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 [[https://trac.ffmpeg.org/wiki/Encode/H.264#crf|H.264 guide]]. 

</WRAP>

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===== References =====

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