mv files: sorry: i am sure this was asked before

[qthesnake]

Hey:

beacause i can't search for words under 3 letters, amd "mv files and ".mv" doesn't give me any result, i got to ask:

what are those large ".mv" files for? i guess they store information for the second pass (is it related to the "back frame process?) but i am not sure...

if someone could give me a short description....

thanx!

[Acaila]

MV stands for Motion Vector.

Each macroblock of a frame is 'tracked' across frames to determine how it moves. Only the difference in motion between frames is stored. These differences are called motion vectors. Motion vectors are in turn quantized to reduce the space they take up and this result is stored for each macroblock.
The first pass calculates these motion vectors because they are important to know for just about everything else it needs to gather information on. The second pass calculates these again to form the final image. So a good way to speed things up is to re-use the motion vectors from the first pass.
However since motion vectors change according to (among other things) the quantizer level and the final encoded previous frame, using the mv data from the 1st pass introduces a slight deviation compared to calculating it anew. This deviation is small enough to be not visible, but the speed gain is substantial.