AVContentKeySession Best Practices

WWDC 2018

FairPlay Streaming Overview

• Introduced in 2015
• Protects HLS streams
• Specifies steps to securely deliver content decryption keys

AVContentKeySession

• Introduced in 2017
• Designed around content decryption keys
  - Simplified key loading process
  - Home for new content protection features
• Great adoption — helps optimize key delivery

AVAssetResourceLoader

How Do I Reduce Playback Startup Delay ?

• Preload keys that you predict might be used
• Batch up key requests — reduce round-trips to key server

Could A key Be Requested Again ? YES

• New keys might be required for decryption 
  ( AirPlay, Lightning Digital AV Adpater )
• Always be prepared to answer redundant key requests

How Do I Preload All Keys ?

• Need key identifier to load key
• Obtain all key identifiers out-of-band
• Advertise session keys ( EXT-X-SESSION-KEY ) in master m3u8
  - Initiate preloading urlAsset.resourceLoader.preloadsEligibleContentKeys = true
• Measuring and Optimizing HLS Performance WWDC 2018

How Can My Live Streams Avoid The Thundering Herd?

• Disperse key request events 👍
• Clients rotate keys at the same time → impulse load on key server
• Load keys before EXT-X-KEY tag appears
• Scale live offering by load balancing key loading requests
• Advances in HTTP Live Streaming WWDC 2017

What is Offline Rentals ?

• Define 2 expiration durations on offline FairPlay Streaming keys
  - Storage duration
  - Playback duration
• Expiration durations are enforced even when the device is offline

How Do I Do Offline Rentals ?

• Use Offline Key TLLV
  - Signaled in CKC used while requesting persistent key

How Do I Do Offline Rentals ?

How Do I Handle Errors While Loading Keys ?

• When something fails…
  - Report error to AVFoundation

• Monitor error logs and address root-cause
• Error Handling Best Practices for HTTP Live Streaming

Common Pitfalls While Delivering Keys

• Taking too long to provide key response
  - Player times out waiting for key repsonse
  - Deliver keys as soon as possible
  - Survey playerItem.accessLogs()
• Using same keys across variants with different HDCP requirements
  - HDCP requirements is signaled inside key response
  - Use multiple key identifiers
• Using persistent keys to answer all key loading requests
  - Persistent keys cannot be shared across devices ( AirPlay )
  - Make sure key loading request accepts persistent keys
  - Minor API changes in iOS 11.2+

Is Persistent Key Accepted As Response?

• Using AVContentKeySession

• Using AVAssetResourceLoader