How DRM works
The video is encrypted when it is packaged for streaming. When a viewer presses play, the player asks a license server for the key. The server checks that the viewer is entitled to the title and returns a license that only that device's protected decryption module can open.
The key is never exposed to the app or the browser page, so the stream cannot be decrypted by copying its address or reading the page's code.
What a DRM license controls
- Whether this device may play the title at all
- How long the license lasts, for example a 48-hour rental
- The maximum resolution, depending on how secure the device is
- Whether output to an external display requires HDCP
- Whether the title may be stored for offline viewing, and for how long
The main DRM systems
Three systems cover almost every device. Widevine, from Google, covers Android, Android TV, Chrome and most smart TVs. FairPlay, from Apple, covers iPhone, iPad, Apple TV and Safari. PlayReady, from Microsoft, covers Windows, Edge, Xbox and many smart TVs.
No single system reaches every device, so a service that wants full coverage uses all three. That is called multi-DRM.
When a streaming service needs DRM
DRM is needed when a rights holder requires it, which studios and sports leagues normally do, and when content is valuable enough that copies would cost you sales. For free or promotional video, signed URLs are usually enough.
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