Bluish Coder

Programming Languages, Martials Arts and Computers. The Weblog of Chris Double.


2008-03-13

Refactoring of Firefox HTML video element patch

I've making some changes to the patch implementing the HTML <video> element for Firefox.

Previously the patch attached to the bug contained the implementation of the video element and a Theora backend implemented using liboggplay.

This required pulling in a large amount of third party library code making it more difficult to get reviews for the patch and to get feedback on the changes required for the video element itself. To hopefully fix this I'm changing bug 382267 to only include the video element implementation with no video decoders.

Applying the patch from that bug to the Firefox trunk source and building with the --enable-video option will provide support for <video> but all videos will fail to load due to not having a supported decoder. This is obviously not very useful but will hopefully make the patch easier to get reviewed and landed.

I've added bug 422538 which will contain support for decoding Theora videos. This is the code taken out of the original bug. Applying the patch from this bug on top of the video element patch and building with --enable-ogg will give <video> element support that can play Theora videos.

As part of the refactoring I've made it easier for different video decoder backends to be implemented. There is an abstract class with pure virtual methods that can be inherited from. I have a 'work in progress' implementation of a GStreamer backend that I'll write about later and attach a patch to bug 422540. This backend allows playing any video format supported by GStreamer. I've tested it with the Fluendo H.264 decoder and it plays fine. Keep an eye on the bug if you're interested in this.

An advantage of this refactoring is that embedders of Gecko) can choose a video backend that suits their purposes (for legal or other reasons they may choose not to have support for a particular format), or implement their own.

Currently the interface for implementing video decoder backends is a C++ abstract class. I'm considering using XPCOM so that implementations can be built and dynamically loaded. This could allow extensions to be written containing video backends that will work with the <video> element. One of the questions asked of me at the W3C video on the web workshop was whether third party providers of DRM enabled codecs could leverage the <video> element. This could provide a pathway to doing that.

The git repository will be restructured so that the 'master' branch contains the <video> element support only. The 'ogg' and 'gstreamer' branches will contain the implementations of the backends.

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