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About the OpenTok scalable video feature

Scalable video can greatly improve the quality of video in multi-party sessions. Using this feature, a client automatically publishes a multi-quality video stream, composed of multiple video resolutions and frame rates. This allows simultaneous subscribing endpoints to consume different video resolutions and frame rates.

The scalable video feature is only available in routed sessions (sessions that use the OpenTok Media Router). See The OpenTok Media Router and media modes.

The OpenTok Media Router dynamically switches between different video resolutions and frame rates for a subscriber's stream, as network conditions on the subscribing endpoint change.

You do not need to add any code to use the scalable video feature. The OpenTok Media Router handles the switching of subscriber stream resolutions and frame rates automatically. The OpenTok Media Router turns on this feature when it determines the session will benefit from it based on the topology of clients connected to the session.

Scalable video is only available in streams published by clients that use:

• The OpenTok iOS SDK

• The OpenTok Android SDK

• The OpenTok Windows SDK

• The OpenTok Linux SDK

• OpenTok.js in Chrome, Opera, Edge, and Safari

It is only supported for VP8 streams. It is not supported for H.264 streams.

For screen-sharing streams, you need to enable scalable video for the published stream:

• In OpenTok.js, for streams that have the video source set to "screen", set the scalableScreenshare option for the OT.initPublisher() method.

• In the OpenTok Android SDK, for streams that have the video type set to PublisherKitVideoTypeScreen, use the PublisherKit.Builder.scalableScreenshare() method.

• In the OpenTok iOS SDK, for streams that have the OTStreamVideoType set to OTStreamVideoTypeScreen, use the OTPublisherKitSettings.scalableScreenshare property.

• In Windows SDK, for streams that have the VideoSourceType set to Screen, use the Publisher.Builder.ScalableScreenshare property.

• In the Linux SDK, for streams that have the video type set to OTC_PUBLISHER_VIDEO_TYPE_SCREEN, use the otc_publisher_settings_set_scalable_screenshare() function.

By default, scalable video is disabled for screen-sharing streams.

In OpenTok.js, scalable video is enabled by default for streams with a camera or custom video source. To disable scalable video, set the scalableVideo option for the OT.initPublisher() method.

All OpenTok clients can subscribe to scalable video streams. The client SDKs include methods or properties for setting the preferred frame rate and resolution for the stream a subscribing client receives from the OpenTok Media Router:

• In OpenTok.js — Subscriber.setPreferredFrameRate() and Subscriber.setPreferredResolution()

• In the OpenTok Android SDK — SubscriberKit.setPreferredFrameRate() and OSubscriberKit.setPreferredResolution()

• In the OpenTok iOS SDK — OTSubscriberKit.preferredFrameRate and SubscriberKit.preferredResolution

• In Windows SDK — Subscriber.PreferredFramerate and Subscriber.PreferredResolution.

For more information, see this article.