Midivid is identified by the FourCC MV43. Its original website is at:

  http://midivid.com/

  The files Mideo43-p3.dll and Mideo43-p4.dll came from self-installers
  named Mideo43-P3.exe and Mideo43-P4.exe, respectively, except that both 
  of the DLLs were named Mideo43.dll originally. Presumably, the P3 and 
  P4 packages have different SIMD optimizations. The file MV3.DLL comes 
  from a self-installer named "MHACodec Setup.exe".