People keep asking why we don't integrate support for Windows' DirectShow into Firefox so the <video> element can play any media that the user has a DirectShow codec for. Even if a volunteer produces a patch, I would not want to ship it in Firefox in the near future; let me try to explain why.
- Probably most important: we want to focus our energy on promoting open unencumbered codecs at this time.
- Only a very small fraction of Windows users have a DirectShow codec for the most important encumbered codec, H.264. Windows 7 will be the first version of Windows to ship with H.264 by default. Even if millions of people have downloaded H.264 codecs themselves, that's a very small fraction of our users.
- DirectShow is underspecified and codecs are of highly variable quality. Many codecs probably will not work with Web sites that use all the rich APIs of <video>, and those bugs will be filed against us. We probably will not be able to fix them. (Note that the problem is bad enough that in Windows 7, Microsoft isn't even going to allow unknown third parties to install DirectShow codecs.) We could avoid some of this problem by white-listing codecs, but then a lot of the people who want DirectShow support wouldn't be satisfied.
- Many DirectShow codecs are actually malware. ("Download codec XYZ to play free porn!")
- DirectShow codecs are quite likely to have security holes. As those holes are uncovered, we will have to track the issues and often our only possible response will be to blacklist insecure codecs, since we can't fix them ourselves. If we blacklist enough codecs, DirectShow support becomes worthless.
- Each new video backend creates additional maintenance headaches as we evolve our internal video code.
So even if we didn't care about promoting unencumbered codecs and someone gave us a working patch, shipping DirectShow support in Firefox is of limited value and creates tons of maintenance work for us.
Some (but not all) of the same arguments apply to using Quicktime. But if we're going to ship our own video infrastructure for Windows, we save ourselves a lot of trouble by using that infrastructure across all platforms. It saves authors a lot of trouble too, due to less variability across Firefox versions.
Currently no browser or browser plugin vendor is using codec implementations they don't control. Apple does allow third-party codecs to be used with Quicktime in Safari --- but at least they control the framework and the important codecs, and apparently they have made some changes for Web video.