Obs Crop Window: What It Means & How to Use It

Obs crop window refers to the adjustable capture area in OBS Studio that defines which portion of your screen or source is recorded or streamed. You set it by holding Alt and dragging the red handles on any source, and it lets you record only a specific region without cropping the actual source resolution. This guide explains exactly how it works, how to set it up, and how to avoid common pitfalls.

What Exactly Is a Crop Window in OBS?

In OBS Studio, a crop window is the rectangular region of a source (like a display capture, game capture, or window capture) that you choose to keep visible. Everything outside that rectangle is hidden from the output. Unlike resizing a source, cropping changes what part of the source is shown, not just how large it appears. This is useful when you want to show only a specific part of your screen, such as a chat box, a scoreboard, or a section of a game map.

The crop is non-destructive: your original source remains unchanged, and you can adjust or remove the crop at any time. The crop window is defined by four values: left, right, top, and bottom, which represent how many pixels to cut from each edge of the source.

How to Create and Adjust a Crop Window

There are two main methods to crop a source in OBS: using the visual editor or entering numeric values in the properties panel.

Visual Cropping (Alt + Drag)

1. Add a source to your scene (e.g., Display Capture, Window Capture, or Game Capture).
2. Select the source in the preview window.
3. Hold the Alt key on your keyboard.
4. Click and drag one of the red handles on the edges or corners of the source. Dragging inward crops that side; dragging outward expands the crop (if there is extra source area).
5. Release the mouse and the Alt key to apply the crop.

This method is intuitive, but it can be tricky to get exact pixel values. For precise control, use the numeric method.

Numeric Cropping

1. Right-click the source in the sources list.
2. Select Transform > Edit Transform.
3. In the dialog, you will see fields for Left, Right, Top, and Bottom.
4. Enter the number of pixels to crop from each side. For example, to crop 100 pixels from the left, enter 100 in the Left field.
5. Click OK to apply.

You can also access these fields by selecting the source and pressing Ctrl+E (or Cmd+E on Mac) to open the Edit Transform dialog directly.

What Does the Crop Window Do to Resolution and Performance?

When you crop a source, OBS still processes the full source internally, but only the cropped area is sent to the encoder. This means cropping does not reduce the load on your GPU or CPU in most cases – the source is still captured at its original resolution. However, the final output resolution (the canvas resolution) is what matters for your stream or recording. If you crop a source to a smaller area, that area is scaled to fit your output canvas if the source is set to scale to screen.

For example, if you have a 1920×1080 display capture and you crop it to a 1280×720 region, OBS will scale that 1280×720 region up to your canvas resolution (if your canvas is 1920×1080). This can cause blurriness. To avoid that, you can adjust your canvas resolution to match the cropped area, or use a separate scene with a lower resolution.

Common Problems and How to Fix Them

• Alt+drag not working: Make sure you are holding Alt before you click and drag. Also, check that the source is selected, not the scene itself.
• Cropped area looks blurry: This happens when the cropped region is scaled up to a larger canvas. Set your canvas resolution to the same aspect ratio as the cropped area, or use a higher base resolution.
• Can’t crop a game capture: Some games capture in exclusive fullscreen, which may not allow cropping. Try running the game in windowed or borderless windowed mode and use Window Capture instead.
• Crop resets when I change scenes: Crops are saved per source, but if you duplicate a source, the duplicate has its own transform. Make sure you are editing the correct source instance.
• Alt+drag moves the window instead of cropping: On some operating systems, Alt+drag is used to move windows. In OBS, this should work, but if not, try using the numeric method or check your OBS version.

Using Crop Windows for Different Purposes

Crop windows are incredibly versatile. Here are a few common use cases:

• Showing only a game map: Crop a game capture to show just the mini-map in a corner of your stream.
• Removing black bars: If your source has black bars on the sides (e.g., from a 4:3 game), crop them out to fill the screen.
• Focusing on a chat window: Crop a window capture to show only the chat area, not the entire application.
• Creating picture-in-picture: Crop a webcam source to a close-up of your face, then place it over your gameplay.
• Recording a specific UI element: Crop a browser source to show only a donation ticker or a subscriber count.

Comparing Crop Window with Other OBS Transform Tools

Crop window is often confused with resizing and masking. Here’s a quick comparison:

• Crop: Removes parts of the source from the edges. The source’s internal resolution stays the same, but the visible area is reduced.
• Resize (scale): Changes the size of the entire source, including all its content. No content is removed; it is just stretched or shrunk.
• Mask/Filter: Hides parts of the source using a shape (like a circle or a custom image). This is more flexible than a rectangle but can be more complex to set up.

For most purposes, cropping is the simplest and fastest way to show only a specific region. If you need a non-rectangular shape, you would use a mask filter instead.

Frequently Asked Questions

Does cropping a source in OBS affect my recording quality?

Cropping itself does not degrade quality, but scaling the cropped area up to a larger canvas can. If you crop a 1920×1080 source down to 1280×720 and your canvas is 1920×1080, the cropped area will be stretched, causing a loss of sharpness. To maintain quality, set your canvas resolution to match the cropped area’s aspect ratio or use a higher base resolution.

Can I crop a source without holding Alt?

Yes, you can use the numeric method via Transform > Edit Transform or by pressing Ctrl+E. You can also use the Filters panel to add a Crop/Pad filter, which gives you the same control with a slider interface.

Why does Alt+drag not work on my Mac?

On macOS, the Option key (Alt) is used for cropping, but some keyboard layouts or OBS versions may require you to use the Cmd key instead. Check your OBS settings under General > Hotkeys to see the assigned modifier. If it still doesn’t work, use the numeric method.

Can I crop a source in a scene and then move it?

Yes, after cropping, you can move the cropped source by clicking and dragging it (without Alt). The crop remains fixed relative to the source’s position. If you want to move the cropped area within the source, you would need to adjust the crop values again.

Does cropping affect the source’s aspect ratio?

Cropping removes pixels from the edges, which changes the visible aspect ratio. For example, cropping the sides of a 16:9 source will make it more square. This can cause stretching if you then scale it to a different aspect ratio. To avoid distortion, keep the aspect ratio of the cropped area proportional to your canvas.

Final Thoughts on Crop Windows

The crop window is one of the most useful tools in OBS for controlling exactly what your audience sees. Whether you are a streamer, a content creator, or just recording a tutorial, mastering the crop window will give you cleaner, more professional output. Remember to use Alt+drag for quick adjustments, use the numeric editor for precision, and always check your canvas resolution to avoid scaling issues. With a little practice, cropping will become second nature.

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in x | X position | px | 0 | 0
in y | Y position | px | 0 | 0
in w | Width | px | 1920 | 1
in h | Height | px | 1080 | 1
out crop | Crop area | px | w * h | 0