I had the same problem as you, fortunately, found a reason and solution:
With the release of the Flash Player 9 Update that supports H.264, we can now play a subset of the H.264 movie files. The problem is that most H.264 files have an index at the end of the file, which for progressive download means that you need to download the entire file before you can start watching any of the videos.
There is also an Air application - QTIndexSwapper , written by Renan Erickson, which fixes the problem. It works!
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