====== 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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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"
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===== 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 [[https://trac.ffmpeg.org/wiki/Encode/H.264#crf|H.264 guide]].
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===== References =====
https://trac.ffmpeg.org/wiki/Encode/H.264#crf