What does a red line above a transition indicate?

A red line above a transition typically signifies that the transition requires rendering before it can be played back smoothly. This visual cue alerts the editor that the effects, which may include transitions, overlays, or other processes that involve significant processing power or resources, are not yet fully processed by the software and may result in playback issues if attempted without rendering.

When a red line appears, it indicates that the software is still working to compile the changes. Rendering ensures that the applied effects are previewed accurately, providing a smooth playback experience. Thus, the presence of a red line serves as a prompt for the editor to render the timeline or section of video that includes the transition, ensuring that what they see during playback matches the output they intend to share or finalize.