Tuesday, June 29, 2010

Flash and the HTML5 <video> tag

There's been a lot of discussion lately about whether or not the HTML5 <video> tag is going to replace Flash Player for video distribution on the web. We’ve been excited about the HTML5 effort and <video> tag for quite a while now, and most YouTube videos can now be played via our HTML5 player. This work has shown us that, while the <video> tag is a big step forward for open standards, the Adobe Flash Platform will continue to play a critical role in video distribution.

It's important to understand what a site like YouTube needs from the browser in order to provide a good experience for viewers as well as content creators. We need to do more than just point the browser at a video file like the image tag does - there’s a lot more to it than just retrieving and displaying a video. The <video> tag certainly addresses the basic requirements and is making good progress on meeting others, but the <video> tag does not currently meet all the needs of a site like YouTube:

Standard Video Format
First and foremost, we need all browsers to support a standard video format. Users upload 24 hours of video every minute to YouTube, so it's important to minimize the number of video formats we support. Especially when you consider that for each format, we also provide a variety of sizes (360p, 480p, 720p, 1080p). We have been encoding YouTube videos with the H.264 codec since early 2007, which we use for both Flash Player and mobile devices like the iPhone and Android phones. This let us quickly and easily launch HTML5 playback for most videos on browsers that support H.264, such as Chrome and Safari.

Concerns about patents and licensing have prevented some browsers from supporting H.264; this in turn has prevented the HTML5 spec from requiring support for a standard format. We believe the web needs an open video format option. One that not only helps address the licensing concerns, but is also optimized for the unique attributes of serving video on the web. To that end, we’re excited about the new WebM project. Google is open sourcing and contributing the VP8 codec to the WebM effort. Google, Mozilla, and Opera have all committed to support WebM, and we have already started making YouTube videos available in the WebM format. Adobe has also committed to support VP8, the video codec for WebM, in an upcoming Flash Player release.

Robust video streaming
Closely related to the need for a standard format is the need for an effective and reliable means of delivering the video to the browser. Simply pointing the browser at a URL is not good enough, as that doesn't allow users to easily get to the part of the video they want. As we’ve been expanding into serving full-length movies and live events, it also becomes important to have fine control over buffering and dynamic quality control. Flash Player addresses these needs by letting applications manage the downloading and playback of video via Actionscript in conjunction with either HTTP or the RTMP video streaming protocol. The HTML5 standard itself does not address video streaming protocols, but a number of vendors and organizations are working to improve the experience of delivering video over HTTP. We are beginning to contribute to these efforts and hope to see a single standard emerge.

Content Protection
YouTube doesn't own the videos that you watch - they're owned by their respective creators, who control how those videos are distributed through YouTube. For YouTube Rentals, video owners require us to use secure streaming technology, such as the Flash Platform's RTMPE protocol, to ensure their videos are not redistributed. Without content protection, we would not be able to offer videos like this.

Encapsulation + Embedding
Flash Player's ability to combine application code and resources into a secure, efficient package has been instrumental in allowing YouTube videos to be embedded in other web sites. Web site owners need to ensure that embedded content is not able to access private user information on the containing page, and we need to ensure that our video player logic travels with the video (for features like captions, annotations, and advertising). While HTML5 adds sandboxing and message-passing functionality, Flash is the only mechanism most web sites allow for embedded content from other sites.

Fullscreen Video
HD video begs to be watched in full screen, but that has not historically been possible with pure HTML. While most browsers have a fullscreen mode, they do not allow javascript to initiate it, nor do they allow a small part of the page (such as a video player) to fill the screen. Flash Player provides robust, secure controls for enabling hardware-accelerated fullscreen displays. While WebKit has recently taken some steps forward on fullscreen support, it's not yet sufficient for video usage (particularly the ability to continue displaying content on top of the video).

Camera and Microphone access
Video is not just a one-way medium. Every day, thousands of users record videos directly to YouTube from within their browser using webcams, which would not be possible without Flash technology. Camera access is also needed for features like video chat and live broadcasting - extremely important on mobile phones which practically all have a built-in camera. Flash Player has provided rich camera and microphone access for several years now, while HTML5 is just getting started.


We’re very happy to see such active and enthusiastic discussion about evolving web standards - YouTube is dependent on browser enhancement in order for us to improve the video experience for our users. While HTML5’s video support enables us to bring most of the content and features of YouTube to computers and other devices that don’t support Flash Player, it does not yet meet all of our needs. Today, Adobe Flash provides the best platform for YouTube’s video distribution requirements, which is why our primary video player is built with it.

John Harding, Software Engineer,