Synchronized recorded video and text playback - iPhone

Question

I'm a new developer and I want to know if it is possible to record a video and process it so that specific text is displayed above/below or inside the video.

Specifically, my educational app displays random words in a text label at a regular interval, and I want my user to be able to record himself saying those words with the front facing camera. Then I'd like to save that video with the words added to it-- that means that during video playback the user would see all of the words come up as he saw them during recording.

I'm wondering if this text display (and synchronization) are possible.

Does anyone have any suggestions or pointers in the right direction (if this is even possible)?

Answer 1

Apple has a ton of documentation on Core Media Time.

Create a list of times at which you want each word to appear and disappear, then compare those times against the running time of the recording in a timer or frame rate callback, to decide what word to (re)draw onto a view or layer.

Answer 2

As long as the videos are in full (there are no stops at all) and they are recorded at the same frame rate then you just need to find one point that you can find the sync point and the rest will be in sync. Another option is to record the timestamp of when the text you want to appear. That way you can subtract between two texts to get the duration of the text.