Suggestion: Improve Performance with more than one video track

Hey there:
I noticed that the performance drops drastically if there are two video stripes above each other. I think there is room for improvement, at least as long as the upper stripe is 100% opaque. In this case the lower one could just be ignored…

Here is an example where you can see the performance loss as soon as there are two videos stacked on each other:

My System:
Linux Manjaro
ShotCut 16.04.01

Track composting is enabled by default because too many beginners or casual users ask how/why to composite things. Turn it off if you do not need it. It is not enough to determine if the upper video is 100% opaque because every pixel has an alpha value.

For windows setting priority to “above normal” for shotcut.exe improve video playback a lot.
If you want to run shotcut in this priority every time just make a .bat file.

For Linux idk if there’s similar solution.

What are the CPU and hard drive specs for your system? The performance is muct better on my system.

I should also mention that you toggle track compositing by clicking [C] on the track header.

It also occurred to me that you might be thinking: “But my video on the upper track does not have an alpha channel.” Well, it is not that simple because the underlying component has more blending modes than simple “alpha over” that do not depend entirely on alpha channel. Yes, theoretically, it is possible to detect the combination of factors (no alpha and blend mode = over) to automatically disable compositing, but that will require quite a bit of rework and additional signaling in the engine.

On the long to-do list is the ability to manually add a blending effect per-clip for when track compositing is turned off.

Lastly, if you turn off “Realtime” in the Settings menu, then it will use multiple logical processors and try to go faster through parallel processing.

Ok, thanks for the replys!
I use a 6 year old laptop, because my other one is being repaired right now. I know, that this machine is probably not suitable for video editing. But with this low performance, it’s maybe easier to see where there are performance problems, and I think better systems could also profit from tackling them.

When I thought about it I also noticed, that it probably wouldn’t be a quick fix, because of al the combinations you have to take into account. Another solution for smooth playback would be an intermediate format I guess…
Is there something planned like this in the future?