Video Essentials

The WebM Basics


With so much going on in online video, it’s easy to forget that the industry is still in its infancy. The whole online video world can be flipped upside-down in a day, especially if a major company like Google is doing the flipping.

On the first day of Google’s I/O developer conference 2010, the company announced a new format for online video, WebM, which is based on a video codec that Google acquired the year before. With tremendous industry support from the start, it seems certain that WebM will become a dominant format in online video.

If this all has your head swimming, you’ve come to the right place. We spoke to Shawn Carnahan, chief technology office for Telestream, to help sort it out. Telestream is one of the early supporters of the format, and has been involved with Google in supporting WebM in a variety of products. All Telestream products, from desktop level to enterprise, either support WebM now or soon will.

What is WebM?
“WebM is an initiative to create a new video and audio format specifically for use on the Web that meets a number of criteria,” says Carnahan. “It offers comparable quality to other media formats that are out there, and it’s royalty-free, unencumbered by patents and royalty issues.”

That’s the high-level view. The format itself is made of three components, he says: first is a new file format based on an open source project called Matroska. The purpose of the container is to hold the video and audio streams so they can be synched for playback. The container is comparable to a QuickTime or MPEG4 file.

The second component is the audio compression, and for this Google chose another open source project, one called Vorbis or Ogg Vorbis. It’s been out there for a number of years, Carnahan says. “It’s certainly the most popular open source audio codec.” It’s modern in the algorithms it employs and is comparable to AAC, the audio compression most commonly used in commercial releases.

Finally, WebM uses the VP8 video codec, which was developed by On2. Google gained the codec when it acquired On2 last year. During the I/O conference, Google declared VP8 to be open-source and royalty-free.

Why do we need a new video format?
“The main driver for this is to have a format that’s royalty-free,” says Carnahan. “The main components are something that can be employed by anybody, and can be contributed to by the open source community. That’s generally not true of the current patent-encumbered codecs like H.264.”

To understand why this is important, you need to know that HTML5, which is being adopted now, aims to make video a common and easily-used Web component, like text and pictures. For that to happen, people need a format that’s open and free to use.

WebM has the potential to become the most viewable, widest-adopted video format online, Carnahan says.

Don’t think that Google created a new video format just for the sake of creating a new format, he cautions. Nor did it aim to create one with the best fidelity. The goal was to create a video format with the broadest reach, a baseline format that will always be accessible.

What’s the difference between a format and a codec?
“A format is what you’re going to play. A format could use a number of different options for specific codecs. A good example is Flash. People think of it as a format. Flash has used, over the years, a dozen different audio and video codecs. It transitioned from JPG to VP6 to H.264, and most people didn’t need to be aware of the codec used, just if their browser supported the format,” says Carnahan.

A format is a container, then, or a collection. Codec, on the other hand, is short for “encoder/decoder.” It’s an algorithm that can take an uncompressed audio or video signal, Carnahan says, and compress it down to a much smaller amount of data with minimal impact on the quality of that signal. When the stream is received, it decompresses the data to the original picture or sound.

Most codecs are “lossy,” which means they reduce the amount of data at the expense of some audio or image quality. We use them, Carnahan says, because they deliver the kind of compression rates we need to be able to send data.

How’s the quality of WebM?
“Very good,” says Carnahan. “Comparable to H.264, which today is the most advanced of the video codecs. There are some tradeoffs for ease-of-use: the easier you make the algorithm so that it runs on mobile phones, there’s a trade-off in the data rates it generates. VP8 tries to make algorithms easier so they’d run on cell phones, with minimal differences from H.264.”

At least, that’s been the early technical assessment, he says. WebM is within 5 to 15 percent of H.264 in visual quality. So to get a video file looking just as good, it would have to be slightly larger for WebM than for H.264, something he doesn’t think viewers will notice.

How do I start using it?
Get a software application that can take video and output WebM files, Carhahan says. You can find a list of manufacturers that are supporting WebM, as well as all the tools available, at WebMProject.org’s tools page.

Will people confuse WebM and WebMD?
“If you do a Google search, yes,” Carnahan says with a laugh.




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