How to get the original timestamp from MediaRecorder


I want to know the original time stamp of every frame in a mp4 video that is captured by my device. However, in the mp4 file, the embedded time stamp is the delay referring to the first frame.

Essentially, what I want to get is the time stamp filled in the CaptureResult while triggering the CameraCaptureSession.CaptureCallback. The puzzle in front of me is that I don't know which frame is the first frame after mMediaRecorder.start().

Could you help me with that?