AVAssetWriter leaks segment data when used in Swift

Make sure to read my article on AVAssetWriter leaking segment data before exploring this sample project.

Minimal sample to demonstrate memory is leaked when the AVAssetWriterDelegate is implemented in Swift.

All macOS versions since 11 are affected, until Apple fixed it in macOS 13.3 and newer.

Reproduction conditions

• The AVAssetWriter must be configured to output segment data to it's delegate
• The AVAssetWriterDelegate must be implemented in Swift
• The app must run on macOS version 13.2.1 or older

Demonstrating the issue

This repository contains a sample app demonstrating the issue:

• Open the sample project
• Build & run the app
• Hit the "Start" button for one of the variants

You will see the memory steadily increasing when hitting the "Start with leak" button, the other buttons demonstrate a variant with a workaround. You will see the memory usage stabilize after a moment when clicking these buttons.

Workaround

• Use Objective-C to implement the AVAssetWriterDelegate and box the segment data so it's never bridged.
• Deallocate the memory yourselves on macOS version that are affected.

Authors

Nonstrict B.V., Mathijs Kadijk & Tom Lokhorst, released under MIT License.