Use this code on an object it will generate a videPayer, type in the name of video file in Inspectpr
using UnityEngine;
using System.IO;
using UnityEngine.Video;

public class video_on_object : MonoBehaviour
{
private UnityEngine.Video.VideoPlayer videoPlayer;
public string videofile;
public GameObject this_object_cam;

void Start()
{
GameObject cam = this.gameObject;
videoPlayer = cam.AddComponent<UnityEngine.Video.VideoPlayer>();

// Obtain the location of the video clip.
videoPlayer.url = Path.Combine(Application.streamingAssetsPath, videofile);

videoPlayer.isLooping = true;

videoPlayer.Play();
}
}

still not fixed.... 2019.3.5f1... this engine is one step forward two backwards

Guys, if you are reading videos from a url that are hosted on a server that you own you need to give the server the adequate permissions for the webgl app to load external URLs. It's not a Unity issue, but it's something that took me a while to figure it out.

Guys, the videoplayer is a relatively recent feature, is still evolving, if you import your media in your app, the videos are smooth in the editor, absent in the WebGL build, because they were wrongly encoded in the import settings.
If you use video.url, of course, it depends what kind of video and audio codec were used to bake that specific .mp4 / .ogv video and what code did you use in unity also.
Streaming a video from an URL is so different than playing a local resource. Do you agree ?
Anyway WebGL issue is about encoding formats / bit rate. Try to use a lower bitrate for compressing your mp4 (make it larger in the size, not smaller and with a lower bit rate and try again).

Im on unity 2017 and same issue does not play video on webgl at all.

ehhh... I am currently using Unity 2017.1.0b1 and this is definitely not fixed..

My mp4 video are set using url's... they work great in engine... they work great in exe export...

but the whole thing crash when played using the WebGL version...

And its not like video are too big... 3 of them are below 5mb total!

I have been searching all over unity forums, trackers, google, etc for the last 3 hours and I cannot find anything except this bug report...

I think the only difference is that I play mine using the "new" video player component in a canvas and not as a texture on a cube...

I did a search for "Video Player WebGL" in the tracker, went through the first 3 pages... i'm wondering if i should not try and create a small project and create a bug report of my own...