Windows Media encoding is proved in the latest build 4224. Previously, when MediaCoder encoding Windows Media with Microsoft Windows Media Format component, audio and video data are encoded and muxed in one thread (despite the possibility that the component may have its multi-threading approach underlying). Now audio and video are encoded in separated threads, and the encoded streams are multiplexed after encoding process. This will eliminate some WMV encoding problem and bring in better encoding performance on dual-core processors as well as better container flexibility. If you experience problems with the new mechansim, please report.