  High-efficiency video coding (HEVC) encryption has been proposed to encrypt
syntax elements for the purpose of video encryption. To achieve high video
security, to the best of our knowledge, almost all of the existing HEVC
encryption algorithms mainly encrypt the whole video, such that the user
without permissions cannot obtain any viewable information. However, these
encryption algorithms cannot meet the needs of customers who need part of the
information but not the full information in the video. In many cases, such as
professional paid videos or video meetings, users would like to observe some
visible information in the encrypted video of the original video to satisfy
their requirements in daily life. Aiming at this demand, this paper proposes a
multi-level encryption scheme that is composed of lightweight encryption,
medium encryption and heavyweight encryption, where each encryption level can
obtain a different amount of visual information. It is found that both
encrypting the luma intraprediction model (IPM) and scrambling the syntax
element of the DCT coefficient sign can achieve the performance of a distorted
video in which there is still residual visual information, while encrypting
both of them can implement the intensity of encryption and one cannot gain any
visual information. The experimental results meet our expectations
appropriately, indicating that there is a different amount of visual
information in each encryption level. Meanwhile, users can flexibly choose the
encryption level according to their various requirements.
