How to Blur Vertical Video Borders in Kdenlive

This guide provides a step-by-step tutorial on how to use Kdenlive to apply a Gaussian blur effect specifically to the side borders of a vertical video. By duplicating your video track, scaling the background layer, and applying a blur filter, you can easily fill the black pillars of a widescreen aspect ratio for a professional look.

Step 1: Prepare Your Timeline Tracks

To create this effect, you need two identical video tracks stacked on top of each other.

  1. Import your vertical video into the Project Bin.
  2. Drag the vertical video into the V2 (top) track of your timeline. This will be your crisp, foreground video.
  3. Drag the same vertical video into the V1 (bottom) track, directly underneath the first clip. This will become your blurred background.

Step 2: Scale the Background Clip

Next, you must enlarge the background video on track V1 so that it fills the entire width of the widescreen 16:9 frame.

  1. Select the video clip on track V1.
  2. Go to the Effects tab and search for Transform.
  3. Drag and drop the Transform effect onto the clip in track V1.
  4. In the Properties panel for the Transform effect, increase the Size percentage (usually to around 300% or until the video completely fills the width of the screen).
  5. Adjust the X and Y coordinates in the Transform settings if you need to reposition the background image.

Step 3: Apply the Gaussian Blur

Now, apply the blur to the enlarged background track so it does not distract from the main video.

  1. In the Effects tab, search for Gaussian Blur (or simply Blur depending on your Kdenlive version).
  2. Drag and drop the Gaussian Blur effect onto the enlarged clip on track V1.
  3. In the effect properties, increase the blur strength (horizontal and vertical factors) until the background is sufficiently blurred. A value between 20 and 50 usually works best.

Step 4: Fine-Tune the Appearance (Optional)

To make the foreground vertical video pop even more, you can add a subtle shadow or boundary separation.

  1. Select the foreground clip on track V2.
  2. Apply a Position and Zoom or Transform effect to slightly scale down the vertical clip if needed.
  3. You can also search for and apply the Drop Shadow effect to track V2 to create a clean visual separation between the sharp vertical video and the blurred background.