You can do so by following these steps when you are already on a comment box of google docs:
- Right click on the input box where you usually write a text comment
- Select "Send Smart Comments" from the menu
- Select the appropriate type i.e. audio, video or screen
- Once the recording is done, click on Send buton
- This will create a link and insert it in the comment box
- Leave it untouched and send it as a comment
- If the Comment button isn't clickable, just put an extra space at the end of the link