<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>

CC BY-SA 4.0
2020-04-28T14:35:22.040Z
That's a bit of a gotcha. I didn't know that, thanks.
stib
CC BY-SA 4.0
2020-04-26T17:41:05.833Z
2020-04-26T17:41:05.833Z
Tomas
<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>

<ffmpeg><h.264>
ffmpeg with h264 produces smaller file sizes for veryfast preset
Tomas
# ffmpeg with h264 produces smaller file sizes for veryfast preset

(Asked by: username_0 on 2020-04-26)

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.

**Tags:** ffmpeg, h.264


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## 1 answers

### Answer by username_0 on 2020-04-26. Score: 1

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.

> **Comments:**
> **username_1**: That's a bit of a gotcha. I didn't know that, thanks.  

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