http://bugs.winehq.org/show_bug.cgi?id=31029
--- Comment #6 from Vincent Povirk madewokherd@gmail.com 2012-06-27 10:32:38 CDT --- What's the problem when there are multiple encoders that match the pattern? If the file format isn't supported, Initialize will fail, and seeking the stream afterwards won't break an existing decoder.
It doesn't matter what is the stream position when Initialize is called. What matters is that the position is left alone between calls into the decoder after it is initialized.