Add current tag to iOS video

I have a problem adding a label showing the current time on a video, but I don't know where to start Right now I have two options 1, Record video via didOutputSampleBuffer, AVAssetWriterInputPixelBufferAdaptor 2. Record video, then edit video like https: / /developer.apple.com/library/content/samplecode/ReaderWriter/Introduction/Intro.html .

I chose option 2 and manually added AVAssetWriterInputPixelBufferAdaptor but the application crashed (guessed incorrect PresentationTime when adding adapter)

What I want to know is how to draw on a video-like timeline? https://www.youtube.com/watch?v=9mmrBDA1baY