To enable .SRT file logging, in the DJI Go App, choose the MENU option on the right side of the screen for Images and Video. Choose the Video icon and change file type from .MOV the default to .MP4. Choose the Option tool icon and turn ON Video Caption. With that option turned ON, the .SRT files should be saved along with the .MP4 video file on your SD card when you record during a flight.
Based on internal research and customer feedback the following DJI models should support recording video with the .SRT file: