WebM: The video format of HTML 5

WebM originally comprises a container based on Matroska and the VP8 video codec developed by On2 and acquired by Google. Which then created VP9, a better codec, supported by all actors in electronics.
For audio, the free Vorbis codec is used.

The more recent AV1 format support the VP10 codec.

Th WebM project was developed jointly by Google (which brings VP8/VP9), Mozilla and Opera and then main actors of the Web rallied to this format, that will become the codec of the HTML 5 <video> tag.

Manufacturers of graphics processing units (for computer, cameras) will implement the codec: AMD for processors and graphics units, ARM for processors for mobile, Nvidia for GPUs, Intel will includes support to WebM to its chips if the format become popular, Texas Instruments for processors, and many others ...

The leading provider of video in the world, Youtube, has already started to put online videos in the VP8 format. It is possible to see them through a search on the site with an additional parameter:

https://www.youtube.com/results?search_query=trailers&aq=f&webm=1

Obviously you need a compatible browser.

The question of patents

The most common codec, H.264, which is considered better than the open source theora codec is the subject of patents holds by the MPEG/LA which charges very high annual fees for streaming videos in this format.

Note that software patents that restrict utilisation of such codecs are valid only in the U.S. and South Korea.
However it is enough to prohibit the adoption of H.264 by Firefox even if an independent project was launched to a version of Firefox supporting it for the rest of the world.
With the arrival of WebM which is freely licensed, of quality close to § H.264, browsers have a free codec to implement for the <video> tag.

On May 4, 2010, the license has been redefined to separate the copyright on the code that is now under the BSD license, and the patent on the codec that keeps a clause against litigations. This clause prohibits its use for who is suing it for patent infringement.

In March 2013, Google signed an agreement with MPEG LA, which owns the rights to H.264 for patents it holds and which would eventually be used in VP8 and successors, and this free users of VP8 of any constraint when these patents.
This is not an acknowledgment that VP8 infringes on any of the patents, Google said.

VP8 is it a copy of H.264?

When Steve Jobs was asked about what are the plans of Apple with respect to WebM, he just put a link in response to a technical analysis of VP8 (the page linked is now removed).
Go to "Addendum C: Summary for the lazy" for a summary.
Is VP8 better than H.264? This comparison was made by a programmer of H.264. Is it objective?

Actually there are some contradictions in the analysis:

That’s right: this software is even older than x264!

and then:

In short, it seems to have been released too early.

finally:

VP8 is simply way too similar to H.264.

So, the codec is older than H.264, was released too early and finally it is a copy of H.264!

AOMedia Video 1 (AV1)

Comparison between VP8 and H264, or H265 and VP9, is no longer relevant in 2016 as a successor to these format has every reason to prevail, since it is supported by a consortium including Google, Amason, Cisco, Mozilla, Intel, Microsoft, Netflix. Apple is missing from the group as usual.

The new codec is not patents encumbered in the USA, it is expected to eventually provide 50% smaller files than VP9 and H265, with an equivalent compression and decompression speed.

More

The site of the WebM project, to convert a video in that format, provides the FFmpeg encoder with a patch to add VP9 to the list of formats. Since April 2015 it is used by Youtube and increases resolution video with the same bandwidth. But it will be really usable with hardware acceleration coming in graphics cards.
The VP9 SDK lets you add functions for encoding and decoding in the VP9 format to applications.

• Broadway. A JavaScript WebM decoder you can incorporate into your pages.