VdoCipherContent Decryption Module (CDM)
A CDM is the sealed component inside a browser or operating system that performs the actual DRM decryption. It receives licenses, holds content keys, decrypts media, and enforces policy, exposing none of it to the page. Its protection level determines the device's DRM security level and often the resolution a service allows.
What is a Content Decryption Module?
A CDM is the sealed component inside a browser or operating system that performs the actual DRM decryption. Chrome ships a Widevine CDM, Safari a FairPlay CDM, and Edge adds a PlayReady CDM.
How the CDM Works
The CDM receives licenses from the DRM server, holds the content keys, decrypts the media, and enforces the license policy such as expiry and output rules. It does all of this in isolation and exposes none of the keys or decrypted frames to the surrounding web page or app. The player, through EME, only passes messages back and forth; it never sees inside the CDM.
Why the CDM Determines Quality
- Software vs hardware: A CDM can run in software or be hardware-backed inside a Trusted Execution Environment.
- Security level: The CDM's protection level sets the device's DRM security level (for example Widevine L1 vs L3).
- Resolution gating: Services often allow HD or 4K only to hardware-backed CDMs.
For Platform Owners
When a viewer complains that video is stuck at low resolution, the cause is frequently a software CDM (Widevine L3) on their device, combined with a policy that reserves higher resolutions for hardware-backed playback.