how I can edit a plugin that sends a notification to teacher after students
watches the video. This plugin should be installed to Moodle and send a
notification to teacher when students watch the video so, teacher can know how
many students watched the video and warn students who did not watch the video.
who can help me could you show how to do it ?
I think the simplest way of doing this would be to use the Assignment module. And make the submission type "online text". Ask them a question or tell them to type "i watched the video" into the box and then submit.
The assignment module can send you a notification of the submission. See here:
https://docs.moodle.org/27/en/Using_Assignment
If you are concerned that the student has in fact watched the video, its a common concern. The generally accepted answer around here, is that you should test the student's knowledge (of the video). Not the watching of the video. So perhaps turn your activity into a quiz, and embed the video in the description type question. In subsequent questions, test whether they know what they should know.
If that still doesn't satisfy your requirement, you might look at my "Timed Page" plugin that allows you to customize activity completion based on your own JS rules. Its at the bottom of this page:
http://poodll.com/poodll-plus/
