A Look at Open Video

Video and HTML5 Markup

Adapted from - http://diveintohtml5.info/video.html#markup


 

HTML5 gives you two ways to include video on your web page. Both of them involve the <video> element. If you only have one video file, you can simply link to it in a src attribute. This is remarkably similar to including an image with an <img src="..."> tag.

One video file 

<video src="pr6.webm"></video>

Technically, that’s all you need. But just like an <img> tag, you should always include width and height attributes in your <video> tags. The width and height attributes can be the same as the maximum width and height you specified during the encoding process. Don’t worry if one dimension of the video is a little smaller than that. Your browser will center the video inside the box defined by the <video> tag. It won’t ever be smooshed or stretched out of proportion. 

<video src="pr6.webm" width="320" height="240"></video>

By default, the <video> element will not expose any sort of player controls. You can create your own controls with plain old HTML, CSS, and JavaScript. The <video> element has methods like play() and pause() and a read/write property called currentTime. There are also read/write volume and muted properties. So you really have everything you need to build your own interface.

If you don’t want to build your own interface, you can tell the browser to display a built-in set of controls. To do this, just include the controls attribute in your <video> tag. 

<video src="pr6.webm" width="320" height="240" controls></video>

There are two other optional attributes I want to mention before we go any further: preload and autoplay. Don’t shoot the messenger; let me explain why these are useful. The preload attribute tells the browser that you would like it to start downloading the video file as soon as the page loads. This makes sense if the entire point of the page is to view the video. On the other hand, if it’s just supplementary material that only a few visitors will watch, then you can set preload to none to tell the browser to minimize network traffic.

Here’s an example of a video that will start downloading (but not playing) as soon as the page loads: 

<video src="pr6.webm" width="320" height="240" preload></video>

And here’s an example of a video that will not start downloading as soon as the page loads: 

<video src="pr6.webm" width="320" height="240" preload="none"></video>

The autoplay attribute does exactly what it sounds like: it tells the browser that you would like it to start downloading the video file as soon as the page loads, and you would like it to start playing the video automatically as soon as possible. Some people love this; some people hate it. But let me explain why it’s important to have an attribute like this in HTML5. Some people are going to want their videos to play automatically, even if it annoys their visitors. If HTML5 didn’t define a standard way to auto-play videos, people would resort to JavaScript hacks to do it anyway. (For example, by calling the video’s play() method during the window’s load event.) This would be much harder for visitors to counteract. On the other hand, it’s a simple matter to add an extension to your browser (or write one, if necessary) to say “ignore the autoplay attribute, I don’t ever want videos to play automatically.”

Here’s an example of a video that will start downloading and playing as soon as possible after the page loads: 

<video src="pr6.webm" width="320" height="240" autoplay></video>

And here is a Greasemonkey script that you can install in your local copy of Firefox that prevents HTML5 video from playing automatically. It uses the autoplay DOM attribute defined by HTML5, which is the JavaScript equivalent of the autoplay attribute in your HTML markup. [disable_video_autoplay.user.js] 

// ==UserScript==
// @name           Disable video autoplay
// @namespace      http://diveintomark.org/projects/greasemonkey/
// @description    Ensures that HTML5 video elements do not autoplay
// @include        *
// ==/UserScript==

var arVideos = document.getElementsByTagName('video');
for (var i = arVideos.length - 1; i >= 0; i--) {
    var elmVideo = arVideos[i];
    elmVideo.autoplay = false;
}

But wait a second… If you’ve been following along this whole course, you don’t have just one video file; you have three. One is an .ogv file that you created with Firefogg or ffmpeg2theora. The second is an .mp4 file that you created with HandBrake. The third is a .webm file that you created with Firefogg. HTML5 provides a way to link to all three of them: the <source> element. Each <video> element can contain more than one <source> element. Your browser will go down the list of video sources, in order, and play the first one it’s able to play.

That raises another question: how does the browser know which video it can play? Well, in the worst case scenario, it loads each of the videos and tries to play them. That’s a big waste of bandwidth, though. You’ll save a lot of network traffic if you tell the browser up-front about each video. You do this with the type attribute on the <source> element.

Here’s the whole thing:

Three (!) video files 

<video width="320" height="240" controls>
  <source src="pr6.mp4"  type="video/mp4; codecs=avc1.42E01E, mp4a.40.2">
  <source src="pr6.webm" type="video/webm; codecs=vp8, vorbis">
  <source src="pr6.ogv"  type="video/ogg; codecs=theora, vorbis">
</video>

Let’s break that down. The <video> element specifies the width and height for the video, but it doesn’t actually link to a video file. Inside the <video> element are three <source> elements. Each <source> element links to a single video file (with the src attribute), and it also gives information about the video format (in the type attribute).

The type attribute looks complicated — hell, it is complicated. It’s a combination of three pieces of information: the container format, the video codec, and the audio codec. Let’s start from the bottom. For the .ogv video file, the container format is Ogg, represented here as video/ogg. (Technically speaking, that’s the MIME type for Ogg video files.) The video codec is Theora, and the audio codec is Vorbis. That’s simple enough, except the format of the attribute value is a little screwy. The value itself has to include quotation marks, which means you’ll need to use a different kind of quotation mark to surround the entire value. 

  <source src="pr6.ogv" type="video/ogg; codecs=theora, vorbis">

WebM is much the same, but with a different MIME type (video/webm instead of video/ogg) and a different video codec (vp8 instead of theora) listed within the codecs parameter. 

  <source src="pr6.webm" type="video/webm; codecs=vp8, vorbis">

The H.264 video is even more complicated. Remember when I said that both H.264 video and AAC audio can come in different “profiles”? We encoded with the H.264 “baseline” profile and the AAC “low-complexity” profile, then wrapped it all in an MPEG-4 container. All of that information is included in the type attribute. 

  <source src="pr6.mp4" type="video/mp4; codecs=avc1.42E01E, mp4a.40.2">

The benefit of going to all this trouble is that the browser will check the type attribute first to see if it can play a particular video file. If a browser decides it can’t play a particular video, it won’t download the file. Not even part of the file. You’ll save on bandwidth, and your visitors will see the video they came for, faster.

If you follow the instructions in this chapter for encoding your videos, you can just copy and paste the type attribute values from this example. Otherwise, you’ll need to work out the type parameters for yourself.

Task: Create an HTML page with the <VIDEO> tag 

Create an HTML page using the HTML5 Video Tag and videos files you have created
Post a link it to the comments below