VSE render too slow with speedup strings

I recorded a video during my modelling session. I use OBS for record my screen.
Now I have the video, all fine (mp4) but now I want speed up the video, in blender VSE editor add an effect string Speed control, set the Multiply speed to 4 and start the rendering but it is too slow, incredibly slow the video is 33 minutes long, in 20 blender processed only 5 minutes or similar.

My machine is not fast but, usually, I have not problems with VSE rendering (this is the first time I use speed control string). Maybe I did something wrong?