Question / Help How to render only cropped area of window/screen capture?

[Fran3]

I’m using drawing programs like PC Paint or SmoothDraw to create video tutorials like Khan Academy and others for uploading to YouTube and other such sites.
The Issue:
I do not want to capture the entire screen or an entire window
I just want to capture the drawing area of the applications window.
I have learned how to create a “filter” to crop the portion of the window I want to capture
BUT... It still saves the video height and width equal to the entire window size...
So I end up with a lot of black around the edges of the actual drawing area.
The Question:
How to I have OBS save or render out only the portion of the window that I want?
Thanks for any help.

 

[koala]

You need a understanding about the concepts of sources and the canvas in OBS.
The video you output is made from the canvas. If you don't put any sources onto the canvas, you create a black video - the default color.
Usually, you have your canvas size at the monitor resolution. Probably 1920x1080.
If you put a display capture source onto the canvas, or a maximized window capture it occupies the whole canvas, so it looks as if it replaces the canvas, because it has the same dimension as the canvas (1920x1080). In fact, it just overlays everything. The canvas is still present.
If you crop your source, you make it smaller, for example 1700x950. Now the canvas shines through, because the cropped source doesn't occupy the whole canvas any more.

Now you have 3 options to make your cropped source occupy the whole canvas instead of only a part:

• you can make your canvas smaller, so it is only so big as your cropped source. For example 1700x950 in my above example. In this case, the source again occupies the whole canvas and you have no empty areas. The downside of this is that you need to keep the 16x9 aspect ratio with your crop, otherwise your videos will not fit to the hardcoded 16x9 aspect ratio of almost all of the streaming services. And you probably don't get a standard resolution (1080p, 720p. etc.)
• Or you can right-click your cropped source->Transform->Fit to screen to scale your cropped source to the 1920x1080 canvas. It again occupies the whole screen. The downside of this is that your content is scaled, so text and drawings may appear blurry. And you have to keep the 16x9 aspect ratio, otherwise you either get black bars on top and bottom or on right and left of your source. You can avoid this by Choosing Transform->Stretch to screen, but this distorts your source.
• Or you can resize your window so your active area after crop is exactly one of the standard resolutions shown on Youtube. For example, if your monitor has 1920x1080, go for your stream having a resolution of 1280x720. For this, don't maximize your window but instead resize it to perhaps 1350x800 and crop it so that the remaining active area is 1280x720. Make your canvas and output 1280x720 (both Settings->Video->Base (Canvas) resolution and Output resolution). This way, you don't need to rescale your window contents, thus neither get the blur effects of source rescaling.

 

[Fran3]

- Just found out I can press Alt and then drag frame handles to crop to the portion of the window I want to capture.

- Question: Is there an easier way to set canvas size than clicking Settings > Video ?

- Why? After I crop I have to click Settings > Video and then play with the "canvas" settings to get the canvas to near the same size as the cropped area I want to capture.

Thanks for the help !