In the What's new in AVFoundation video, the new AVCaption, AVAssetWriterCaptionAdaptor, AVCaptionConversionValidator, and AVAssetReaderOutputCaptionAdapter were announced, but looks like they're currently only for macOS. They would be very useful for iOS as well. Thanks.
Is there any chance of the new Caption functionality being available for iOS
We encourage you to submit an enhancement request for this feature using the Feedback Assistant. Thanks.