[KSV]

encv = Encrypted Video
enca = Encrypted Audio

it's part of Adobe Flash Access DRM. Flash player have separate module for handling drm which is downloaded while you try to play the protected content for first time. it's similar to indivbox dll method used by Microsoft. as like most drm systems encryption algorithms used are publicly available but the main hurdle is to retrieve the decryption key.

AFAIK currently no public tool or method is available to decrypt those videos.