Designing a universal format for encrypted media

Increasingly, video delivery over the internet is being monetized through advertisement or paid services. Almost all monetized video is delivered encrypted to the clients. Clients are authorized to receive the encryption keys after watching advertisements or based on payments. Although the exact same audio and video compression standards are used, the way media is encrypted is very different in different eco-systems like Adobe Flash, Apple HTTP Live Streaming, MPEG Dynamic Adaptive Streaming over HTTP, etc., making them incompatible with each other. In some cases, it is sample (frame) based encryption while it is packet based in others. Even while using sample based encryption, different parts of a sample are selectively encrypted by different schemes. As encryption algorithms typically use different chaining modes (e.g., Cipher Block Chaining) there is some continuity from one encryption block to another. Although there is considerable overlap between encrypted data, the encryption chains are constructed differently across different formats. The goal of this paper is to define a single mezzanine file format to serve as a Universal Encryption Format that a client platform can implement to playback media from different encrypted video delivery systems. We use some basic encryption characteristics to identify and preserve the chains by storing minimal house keeping information about which part of the data is encrypted, where chains are broken, additional initialization vectors, etc. We design and propose an encryption map that is stored typically with the media sample headers. The map securely and efficiently stores information about encryption runs in terms of sizes, IVs, and offsets. We propose additional optimizations in the format to make the encryption maps compact and the decryption, efficient.