Saturday, June 28, 2008

Is HD video on the Web really HD?

Answer this question:

Which is more important to the visual quality of video on the Web? Is it the lines of resolution or is it the encoded bitrate?

The answer: It's a little bit about both but it's mostly about bitrate. For now.

Here's a simple example to illustrate the answer. A video with 1920 vertical and 1080 horizontal lines of resolution and a bitrate of 500 kbps is going to look awful while the same video with 768 vertical and 432 horizontal lines of resolution with a bitrate of 1.5 mbps is going to look terrific. Both have a widescreen aspect ratio of 16:9 but the smaller resolution will look much better.

The simple truth is that we are all so accustomed to bad video on the Web that anything that looks really good seems like it is HD. But HD on the Web is really no different, technically, than HD on your television monitor.

Just like your television monitor, you need four primary elements to view true HD video. First, you need an HD monitor that is capable of displaying 1920 x 1080 video. Second, you need video that is streaming at 1920 x 1080 lines of resolution. Third, you need the power to process all of that data - enough power that the video plays smoothly without skipping frames and stuttering. Finally, you need a bitrate that is consistent with HD video. That bitrate needs to be in the 7 to 10 mbps range. If any one of those elements is missing, then the video is not HD.

I'll assume you've seen the videos at the iPlayer site. If you have a 2 mbps Internet connection, than iPlayer's bandwidth detection has delivered a 1.5 mbps video to you. ( I've uploaded a 500 kbps, 1.0 and 1.5 mbps version of each video). You'll probably agree that the video quality is as good as or better than anything you've ever seen on the Web. Those videos all started out at an HD resolution - most at 1920 x 1080. However, because I know that while you may have an HD monitor, you probably do not have a 7 - 10 mbps Internet connection and thus cannot view true HD. Also, chances are your machine does not have the processing power to display all those lines without skipping frames. So, when I encoded those videos from their original H264 codec to Flash VP6-FLV using On2 Flix Pro, I used a common denominator, 3, and divided both numbers by 3 creating a resolution of 640 x 360. It didn't matter the common denominator so long as I used the same number on both the vertical and horizontal and so long as it reduced the lines to something more compatible with the bit rates I was planning on deploying. I've experimented enough to have learned that a 640 x 360 video encoded at 1.5 mbps will look terrific.

By the way, the iPlayer screen at iPlayerHD.com is 768 x 432 which is a 16:9 aspect ratio. Because iPlayer respects all aspect ratios, my 640 x 360 videos fit neatly in the player screen.

So, there you have it. Until we all have really fast Internet connections and Core Duo processors, we'll need to lower our video resolutions and increase our bit rates if we are to deliver an exceptional video experience to our website visitors.

Of course increasing bitrates and delivering all those bits uninterrupted requires a streaming provider like iPlayer which delivers at up to 3 mbps. And with iPlayer's bandwidth detection, you'll deliver the appropriate bitrate video to each of your site visitors. If you're not already an iPlayer subscriber, perhaps its time you took it out for a spin?

Next up: Bandwidth detection and how it works.

No comments: