Uploading the Video into My Map from Google would be by using YouTube facility, so create your own YouTube channel for uploading the video.
Step 1 : Go to the map
Step 2 : Select the location point which you would like to add a video over
Step 5 : The video will be set up on the location point and then click Save the details
Note : No any more support upload video to location point directly or through google drive, Just support YouTube Video.