How the speed it up a portion of a video, and also all of it? I just started yesterday with Blender, so this is maybe a basic question. I have already seen how to speed it a whole video using "effect strip - speed control". The problem I am trying is when I try to speed it up only a portion of a video, or when trying to speed up a whole video which has different portions. At the moment my project looks like this



As you can see my video has five sequences. Each sequence uses 2 videos which I am putting side to side (one uses 50% of the screen left, the other 50% right). That's why I have those transforms, and then the alpha over, and then the text just to add some caption. I don't know if there is a better way to do this. This video runs at real-time, and it produces what I expected to get. The problem is when I try to speed it up, like by a factor of 4.

Now here is how I try to speed up the whole video:



I chose individually each alpha overlay and added the speed control. Then I moved on top the text, and when I click render animation, it looks fine, but I have some problems with the output video. Using the workflow from above, it produces a video where each segment has everything sped up in the first 15s, and then the following 45s are a static image of the last frame.

I also tried lowering the total frames of the video from 9000 to 2250 (that should be the frames when it is speed x4), but that basically produces a video of 15s first video speed up, then 45s static image, then 15s of the following video, and then it stops.

So my problem is that I don't really know how to speed it parts of a video, or a video as a whole which is composed by parts. When dealing with only 1 video, using speed control I know how to do it. But when working with parts, I dont.
The video gets sped up as you see but it does not affect the length of the strip.  I do not know a way to automate the process but you need to shrink the length of each strip that you are speeding up.  In your case, you are speeding it up by a factor of 4 so you need to make each strip 1/4 of the original length.

Then you need to move all the strips together so there is no space between them.

I did a search on Youtube using this -  blender vse video speed up

and found this video:  https://www.youtube.com/watch?v=NrX1sK_ZQqs

I hope that helps.