After downloading the zip version of FFmpeg 0.6.2, the content should be extracted to a folder called FFmpeg. This folder can be replaced with the folder FFmpeg, which already exists in X:\PortableApps\AudacityPortable\App. To note however is, that this exchange only should be performed for Audacity 1.3.13 or later.
its greatly appreciated Hopefully ffmpeg-mt gets finalised and is cross compatable with the non -mt ffmpeg.
On 21 March 2011 ffmpeg-mt, the multithreaded decoding branch, has been merged into FFmpeg (see the News from March 21, 2011 of the FFmpeg Homepage). Thus, this branch in the above-mentioned FFmpeg library 0.6.2 is included. So FFmpeg can now decode an audio file under use of multiple processor cores. Unfortunately Audacity is not written to take advantage of multi-core CPUs.
so i know they have been merged. this will be most interesting. Also the FFMPEG team got served if you go to their site their logo supposidly violated someone's copyright.