user11789: Fiddling with the h264 and h265 params I found both keyint and min-keyint settings.
Setting keyint shouldn't force the codec library to use exactly that frame interval?
Do min-keyint have something to do with scene detection and if set it take priority over keyint plain setting ?
TL;DR: I found that h265 default settings are keyint=250 and min-keyint=25 ... what I should expect from that? A fixed length GOP or a variable length one?

user1871: See these two links:
1) MeGUI/x264 Settings for an explanation of the parameters like keyint.
2) About --keyint --min-keyint and --scenecut for a discussion at Doom9 about how they interact, specifically

--keyint is the maximum interval. x264 will insert key frames earlier if it deems them beneficial, e.g. due to a scene change. From my
  experience the majority of key frames are in place because of the
  properties of the video, not because keyint was reached. The larger
  --keyint is the smaller the impact on overall key frame placement should be.


11789: <p>Fiddling with the h264 and h265 params I found both <strong>keyint</strong> and <strong>min-keyint</strong> settings.</p>

<p>Setting keyint shouldn't force the codec library to use exactly that frame interval?</p>

<p>Do min-keyint have something to do with scene detection and if set it take priority over keyint plain setting ?</p>

<p>TL;DR: I found that h265 default settings are keyint=250 and min-keyint=25 ... what I should expect from that? A fixed length GOP or a variable length one?</p>
 1871: <p>See these two links:</p>

<p>1) <a href="https://en.wikibooks.org/wiki/MeGUI/x264_Settings" rel="nofollow">MeGUI/x264 Settings</a> for an explanation of the parameters like keyint.</p>

<p>2) <a href="http://forum.doom9.org/showthread.php?t=165197" rel="nofollow">About --keyint --min-keyint and --scenecut</a> for a discussion at Doom9 about how they interact, specifically</p>

<blockquote>
  <p>--keyint is the maximum interval. x264 will insert key frames earlier if it deems them beneficial, e.g. due to a scene change. From my
  experience the majority of key frames are in place because of the
  properties of the video, not because keyint was reached. The larger
  --keyint is the smaller the impact on overall key frame placement should be.</p>
</blockquote>
