user23676: I am experimenting with ffmpeg and x264 codec. And I have found some unexpected behaviour.
I am encoding video with parameters CRF 23, high profile and changing preset.  Documentation says:

for constant quality encoding, you will simply save bitrate by choosing a slower preset.

And I am using CRF, so it should be this particular quote. So how is possible that I have achieved the smallest file for veryfast preset?
medium    256MB
fast      261MB
faster    235MB
veryfast  209MB
superfast 324MB

What am I missing? BTW another comparison have similar results.

user23676: I was able to find an answer. https://stackoverflow.com/a/14308561/941493.
In the nutshell, CRF calculation is also affected by preset so the same CRF number is not the same with different presets. Based on some developer difference can be mostly ignored.

23676: <p>I am experimenting with ffmpeg and x264 codec. And I have found some unexpected behaviour.</p>

<p>I am encoding video with parameters CRF 23, high profile and changing preset.  <a href="https://trac.ffmpeg.org/wiki/Encode/H.264" rel="nofollow noreferrer">Documentation</a> says:</p>

<blockquote>
  <p>for constant quality encoding, you will simply save bitrate by choosing a slower preset.</p>
</blockquote>

<p>And I am using CRF, so it should be this particular quote. So how is possible that I have achieved the smallest file for <code>veryfast</code> preset?</p>

<pre><code>medium    256MB
fast      261MB
faster    235MB
veryfast  209MB
superfast 324MB
</code></pre>

<p>What am I missing? BTW another <a href="https://write.corbpie.com/ffmpeg-preset-comparison-x264-2019-encode-speed-and-file-size/" rel="nofollow noreferrer">comparison</a> have similar results.</p>
 23676: <p>I was able to find an answer. <a href="https://stackoverflow.com/a/14308561/941493">https://stackoverflow.com/a/14308561/941493</a>.</p>

<p>In the nutshell, CRF calculation is also affected by preset so the same CRF number is not the same with different presets. Based on some developer difference can be mostly ignored.</p>
