Use the audio fallback API to dynamically prioritize audio in response to network quality.

Enabling and disabling audio-only fallback

To enable publisher audio fallback, set the OTPublisherKitSettings.publisherAudioFallbackEnabled property when creating the publisher.

// Enable publisher audio fallback
let publisherSettings = OTPublisherSettings()
publisherSettings.publisherAudioFallbackEnabled = YES

// Enable publisher audio fallback and disable subscriber audio fallback
let publisherSettings = OTPublisherSettings()
publisherSettings.publisherAudioFallbackEnabled = YES
publisherSettings.subscriberAudioFallbackEnabled = NO

// Enable subscriber audio fallback and disable publisher audio fallback
let publisherSettings = OTPublisherSettings()
publisherSettings.publisherAudioFallbackEnabled = NO
publisherSettings.subscriberAudioFallbackEnabled = YES

To enable and disable subscriber audio fallback (for all subscribers to the stream), set the OTPublisherKitSettings.subscriberAudioFallbackEnabled property when creating the publisher. Subscriber audio fallback is only supported in routed sessions (sessions that use the Vonage Video Media Router). Subscriber audio fallback is enabled by default (in routed sessions) for streams with a camera video source.

Audio fallback events

When publisher audio fallback is enabled, the PublisherKitDelegate object will send the following messages pertaining to publisher audio fallback-related events:

• [OTPublisherKitDelegate publisherVideoDisableWarning:] — Called when the Publisher determines that the stream quality has degraded and the video will be disabled if the quality degrades more.
• [OTPublisherKitDelegate publisherVideoDisableWarningLifted:] — Called when the Publisher determines that the stream quality has improved to the point at which the video being disabled is not an immediate risk.
• [OTPublisherKitDelegate publisherVideoDisabled:reason:] — Called when the Publisher determines that the stream quality has degraded and the outgoing video transport has been disabled. Note: while the video is disabled, the Publisher still displays the publisher video (such as the camera image) in the publishing client's UI.
• [OTPublisherKitDelegate publisherVideoEnabled:reason:] — Called with reason "quality" when the Publisher determines that the stream quality has improved and outgoing video transport has been re-enabled. For example the following code handles the related events (so that you can provide your own user interface notifications):

func publisherVideoDisableWarning(_ publisher: OTPublisherKit) {
  // Custom action — for example, add custom UI notification
}

func publisherVideoDisableWarningLifted(_ publisher: OTPublisherKit) {
  // Custom action — for example, remove custom UI notification
}

func publisherVideoDisabled(_ publisher: OTPublisherKit, reason: OTPublisherVideoEventReason) {
  // Custom action — for example, add custom UI notification
}

func publisherVideoEnabled(_ publisher: OTPublisherKit, reason: OTPublisherVideoEventReason) {
  // Custom action — for example, remove custom UI notification
}

From the subscriber’s perspective, the following events indicate that audio fallback has occurred. Although these events are tied to the subscriber, they can occur both due to subscriber audio fallback and as a consequence of publisher audio fallback. In other words, the difference between publisher and subscriber audio fallback is that, in the publisher case, the publishing client may trigger the audio fallback based on its own stream degradation, which is why additional publisher-side events are dispatched. For subscriber audio fallback, the Vonage Video Media Router assesses network degradation affecting the subscriber. In both cases, upon publisher or subscriber audio fallback, subscriber events are always dispatched to indicate that audio fallback has occurred for the receiver.

When subscriber audio fallback occurs, the SubscriberKitDelegate object will send the following messages pertaining to subscriber audio fallback-related events:

[OTSubscriberKitDelegate subscriberVideoDisableWarning:] — Called when it is determined that the stream quality has degraded and the video will be disabled if the quality degrades more. [OTSubscriberKitDelegate subscriberVideoDisableWarningLifted:] — Called when it is determined that the stream quality has improved to the point at which the video being disabled is not an immediate risk. [OTSubscriberKitDelegate subscriberVideoDisabled:reason:] — Called when it is determined that the stream quality has degraded and the outgoing video transport has been disabled. Note: while the video is disabled, the Subscriber still displays the subscriber video (such as the camera image) in the publishing client's UI. [OTSubscriberKitDelegate subscriberVideoEnabled:reason:] — Called with reason "quality" when it is determined that the stream quality has improved and outgoing video transport has been re-enabled.

For example the following code handles the related events (so that you can provide your own user interface notifications):

func subscriberVideoDisableWarning(_ subscriber: OTSubscriberKit) {
  // Custom action — for example, add custom UI notification
}

func subscriberVideoDisableWarningLifted(_ subscriber: OTSubscriberKit) {
  // Custom action — for example, remove custom UI notification
}

func subscriberVideoDisabled(_ subscriber: OTSubscriberKit, reason: OTSubscriberVideoEventReason) {
  // Custom action — for example, add custom UI notification
}

func subscriberVideoEnabled(_ subscriber: OTSubscriberKit, reason: OTSubscriberVideoEventReason) {
  // Custom action — for example, remove custom UI notification
}