AES-128 is a highly secure encryption algorithm, and is the only publicly-available encryption algorithm used by the NSA for top secret information. Content encrypted with Advanced Encryption Standard algorithm with 128-bit cipher block size cannot be practically decrypted by brute force attacks.
DRM systems use AES-128 encryption when packaging the video files for streaming. Encryption is only one part of protecting videos. Along with AES-128 encryption, DRM systems also provide a secure mechanism by which content keys are delivered to the user device.
Decrypting the videos on user devices without making the content keys accessible to the end user is the bigger challenge in protecting premium videos. VdoCipher implements Widevine, Playready and Fairplay DRM systems. These Digital Rights Management systems ensure that the content keys used for decrypting the video are not available outside the trusted Content Decryption Module in the browser/ device.
The secure handling of content keys is the main difference between content that has just been encrypted using AES-128, and content that is protected by a DRM system. Mere AES-128 encryption is the cybersecurity equivalent of using a state-of-the-art lock for your home, only to leave the keys under the doormat