Every media player I've seen suffers the same two issues related to rescaling:
1) The user has no control over the rescaling method used (linear, Hermite, Mitchell-Netravali, Catrom, Lanczos etc.)
2) If the player is being run in a virtual machine, or if graphics drivers are not installed, the player falls back to nearest-neighbor resizing
This indicates to me that the rescaling is being done by the graphics card. Why not allow the player to perform the rescaling? This would allow both of the above problems to be solved.