example. Source video resolution is 1280x720.
I adjusted the frame as I need.
Can I quickly, without calculating resolution, without calculation aspect ratio, without changes Project Settings - get a render with a new output resolution, without black bars?
How do people solve this problem?
By not creating it for themselves. Editing video is not like editing still images. You start with the frame size and aspect ratio you want to produce, then fit your source material to that, not vice versa.
I don’t know why you posted this, “deleted” it, then reposted it with an arbitrarily different title - but please don’t do that.
video - a set of sequential images
You’re probably having trouble imagining how to implement this, or how it’s implemented in other programs.
One of many scenarios:
I need to create a Video Sticker for Telegram. However, their rules allow for arbitrary frame widths
Why should I leave black bars if I can discard unnecessary information? This will not only make the video look more pleasing, but also improve the quality of the compressed video slightly.
Step by step: I’m taking a video source recorded on a phone camera, let’s say it’s a 9:16 aspect ratio (vertical). This means resolution and aspect ratio are known in advance.
However, I need to reduce the frame’s top and bottom, because it contains useless information: I just need to zoom in the frame. Accordingly, the sides will move apart and the width will become larger.
As a result, I can’t know in advance what the final aspect ratio will be.
If you’ve never encountered this, perhaps you’re an inexperienced video editor user. And in the future, you’ll have to tackle more complex video editing tasks. If you’re completing the client’s task, they’re setting the conditions FOR YOU.
NOT you. If you set conditions, the client will find another contractor. The true sign of skill and professionalism is not setting your own conditions, but fulfilling all the client’s requirements. You understand this well, right?
I have to solve this problem with routine manual adjustments and calculations. But as we know, people did calculations and adjustments before computers were invented.
In the above case, the videocontent is adjusted to the following conditions: height = 512 pixels; width = arbitrary, but no more than 512 pixels. It requires some extra movement, but it can be done to meet the requirements.
In another case, you’ll simply need to discard excess pixels, avoiding destructive zooming. This is called a “true crop.” In this case necessary to avoid picture stretching algorithms in order to have as little impact on image quality as possible. I can’t imagine what Kdenlive can offer at this stage of development for this case 
We should probably make it technically impossible for users to do this. What do you think?
Will you ask every user “to do this” or “not to do that”? Only if such requests make you happy.
Set the “boundaries” you require for all users. As is the case on other platforms.
If you’d like, I’ll contact the administration and we’ll try to discuss the issue in more detail.
No need to get testy here.
If you know that your source material is 9:16, and the requirements are that one side is 512 pixels and the other can be the same or less, you can set your project dimensions to 288x512 (also 9:16). Then importing 9:16 material fits the project dimension and there is no need to crop.
Of course, if you import footage with a different aspect ratio, you need to zoom (and potentially pan) to eliminate the unavoidable black bars.
I guess you want Kdenlive to adjust the render aspect ratio automatically to eliminate black bars, almost like Handbrake does. Correct?
You can call it whatever you want, but unless you are going to go around resizing everybody’s screens - if you don’t target standard video display sizes. it’s going to happen when people watch your video.
Your decision, if you actually really care about quality - which if you’re targeting some tiny portion of the user’s display you patently don’t - is do you want to do that processing at render time, when you can spend the time to do it as well as possible - or at playback time, when you have to trade quality for speed to achieve real-time playback.
If your mental model of video is “a set of sequential images”, then you’re probably having trouble imagining how this all really works.
