Enhanced seek works quite differently with VP6 video stream
that with Sorenson.
With Sorenson, FMS calculate the frame you request. It
generates a keyframe in that position, followed by the regular
difference frames.
With Vp6 stream, FMS does not calculate the intermediate
keyframe anymore. To enhance scalability, programmers have decided
for a different approach to the problem: FMS send the previous
keyframe and then the intermediate difference frames changing on
the fly the timestamp to the same, starting value. In this way, the
player is forced to decode, as fast as it can, the frame sequence
till the frame to which you have seeded. Starting from this frame,
the movie play at the default rate. in short, it is the flash
player who decode the stream till the required seeked frame. This
approach may, sometime, leads to strange behaviours.