If you write a script for your video, that can serve as your transcript. If you veered away from the script, there are a variety of free programs and websites that will convert the audio from your video and create a text transcript
One of the easiest ways to create an automatic transcription is with Google Docs. You can always play your completed video and have Google “listen” to the video while it plays.
Below is a tutorial on using Google Docs to create a transcription: