user11787: I need to speed up video by a factor of 4x, but do not want to drop the frames and instead average them. I.e. each 4 frames are averaged, and produce 1 output frame. Target frame-rate stays the same, so video is now 4 times faster. 
Is there a way to do so in ffmpeg?

user2585: I use these commands:
4x speedup:
ffmpeg" -r 60 -i "inputfile.mp4"  -vf "tmix=frames=4:weights='1',select='not(mod(n\,4))',setpts=0.25*PTS" -c:v libx265 -an -x265-params crf=25 "outputfile.mp4"

16x speedup:
ffmpeg" -r 60 -i "inputfile.mp4"  -vf "tmix=frames=16:weights='1',select='not(mod(n\,16))',setpts=0.0625*PTS" -c:v libx265 -an -x265-params crf=25 "outputfile.mp4"

The "-r 60" parameter is used to specify the source file fps.
The "crf=25" parameter define the encoding quality (lower number = higher quality = higher size)

user1871: ffmpeg with this filterchain does it:
ffmpeg -i input -vf "tblend=average,framestep=2,tblend=average,framestep=2,setpts=0.25*PTS" -r srcfps -{encoding parameters} output

srcfps should be replaced with your input's framerate.

11787: <p>I need to speed up video by a factor of 4x, but do not want to drop the frames and instead average them. I.e. each 4 frames are averaged, and produce 1 output frame. Target frame-rate stays the same, so video is now 4 times faster. </p>

<p>Is there a way to do so in ffmpeg?</p>
 2585: <p>I use these commands:</p>
<p>4x speedup:</p>
<pre><code>ffmpeg&quot; -r 60 -i &quot;inputfile.mp4&quot;  -vf &quot;tmix=frames=4:weights='1',select='not(mod(n\,4))',setpts=0.25*PTS&quot; -c:v libx265 -an -x265-params crf=25 &quot;outputfile.mp4&quot;
</code></pre>
<p>16x speedup:</p>
<pre><code>ffmpeg&quot; -r 60 -i &quot;inputfile.mp4&quot;  -vf &quot;tmix=frames=16:weights='1',select='not(mod(n\,16))',setpts=0.0625*PTS&quot; -c:v libx265 -an -x265-params crf=25 &quot;outputfile.mp4&quot;
</code></pre>
<p>The &quot;-r 60&quot; parameter is used to specify the source file fps.<br />
The &quot;crf=25&quot; parameter define the encoding quality (lower number = higher quality = higher size)</p>
 1871: <p>ffmpeg with this filterchain does it:</p>

<pre><code>ffmpeg -i input -vf "tblend=average,framestep=2,tblend=average,framestep=2,setpts=0.25*PTS" -r srcfps -{encoding parameters} output
</code></pre>

<p><code>srcfps</code> should be replaced with your input's framerate.</p>
