The track identifier of the video composition when a single source frame should be displayed for the duration of the instruction.
- iOS 7.0+
- macOS 10.9+
- Mac Catalyst 13.0+
- tvOS 9.0+
If for the duration of the instruction, the video composition result is one of the source frames, this property returns the corresponding track ID. The compositor won't be run for the duration of the instruction and the proper source frame is used instead.
The dimensions, clean aperture and pixel aspect ratio of the source buffer are matched to the required values automatically.