Examples of how to convert a video file to a MediaStream where it can be sent via WebRTC. See webrtcHacks post for full details, commentary, and comparisons.

• getDisplayMedia of pop-out video file - load a video file into a pop-up and use getDisplayMedia for capture.
• VideoElement Capture Stream - capture the video and audio directly from a video element. The audio is captured using the Web Audio API and combined with the video stream to create a MediaStream.
• VideoElement Capture Stream with WebAudio - same as above, but experimenting with using WebAudio for local audio control.
• Canvas Capture + Web Audio - write a source video to a canvas and then use canvas.captureStream() to capture the video with Web Audio API to capture the audio.
• WebCodecs - load a video file and use WebCodecs to convert it to a MediaStream

• getDisplayMedia of pop-out video file - load a video file into a pop-up and use the getDisplayMedia for capture.
• VideoElement Capture Stream - capture the video and audio directly from a video element. The audio is captured using the Web Audio API and combined with the video stream to create a MediaStream.
• VideoElement Capture Stream with WebAudio - same as above, but experimenting with using WebAudio for local audio control.
• Canvas Capture + Web Audio - write a source video to a canvas and then use canvas.captureStream() to capture the video with Web Audio API to capture the audio.
• WebCodecs - load a video file and use WebCodecs to convert it to a MediaStream

Big Buck Bunny video converted to 640x360 at 30 fps from peach.blender.org.