Mask Multiple Layers Simultaneously in Kdenlive

This article provides a step-by-step guide on how to use the “Region” composition transition in Kdenlive to mask multiple video layers simultaneously. By using this technique, you can apply a single alpha mask or shape to several video tracks at once, eliminating the need to duplicate masks and keeping your editing timeline clean, organized, and efficient.

Understanding the “Region” Composition in Kdenlive

In Kdenlive, the Region composition restricts the visibility of a track to the alpha channel (transparency) or shape of another target track. Unlike standard masks that only apply to a single clip, the Region transition can be applied to multiple tracks, routing them all to reference a single master mask track.

Step-by-Step Guide to Multi-Layer Masking

Step 1: Arrange Your Timeline Tracks

To mask multiple layers, you must stack your tracks correctly. Place your mask source on the top track, and the videos you want to be masked on the tracks below it.

1. Track V3 (Top): Place your mask here (this can be a black-and-white image, a title clip with a shape, or a video with an alpha channel).
2. Track V2 (Middle): Place your first video clip.
3. Track V1 (Bottom): Place your second video clip.
4. Track V0 (Optional): Place your background layer that should remain unmasked.

Step 2: Apply the Region Transition to the First Video Track

1. Hover your mouse over the bottom-left corner of the clip on Track V2 until the red circle pointer appears.
2. Click to add a composition transition. By default, Kdenlive may apply “Wipe” or “Composite and Transform”.
3. Select the transition block in the timeline to open the Properties panel.
4. Change the transition type to Region (or Composite with the “Region” option enabled, depending on your Kdenlive version).
5. In the transition properties, set the With track (or target track) option to Track V3 (your mask track).

Step 3: Apply the Region Transition to Subsequent Video Tracks

To apply the same mask to Track V1 without duplicating the mask clip:

1. Click the bottom-left corner of the clip on Track V1 to add a transition.
2. Select the transition and change its type to Region.
3. In the Properties panel, set the With track option to Track V3 (the same mask track).

Both Track V2 and Track V1 are now bound to the mask on Track V3. Any visual assets on these two tracks will only be visible within the boundaries defined by the mask on the top track.

Tips for Fine-Tuning Your Mask

• Inverting the Mask: If you want the video to appear outside the mask shape instead of inside it, look for the Invert checkbox in the Region transition properties panel.
• Moving the Mask: If you animate or move the mask clip on Track V3 using keyframes (such as a Transform effect), both underlying video layers will automatically follow the new animated boundaries of the mask.