Adding text subtitles to video track (in Swift) fails with error code -11841

Question

I have been struggling with adding text subtitles to videos for a while. I have added some links that I referred in detail, but they are not helping.

In below code, I a

Answer 1

You failed to insert trackID when creating layer instruction. Try :

let videolayerInstruction : AVMutableVideoCompositionLayerInstruction = AVMutableVideoCompositionLayerInstruction(vtrack)