Client Observability: iOS

The Vonage Video SDK exposes detailed stream-quality metrics through a high-level statistics API—recommended for most use cases—which provides audio, video, network, and sender-side statistics in a unified, session-aware form that remains stable across peer-connection transitions. For advanced debugging, the SDK also offers access to the raw WebRTC stats report, which reflects unprocessed peer-connection data.

The SDK also exposes network condition metrics that provide a high-level assessment of connection health for both publishers and subscribers. These metrics include a network condition score, the reason driving that score, and—for subscribers—a degradation source indicating which side of the connection is responsible for any observed issues. See Network condition and degradation source for details.

Audio, Video and Media Link Statistics API

The Vonage Video iOS SDK sends periodic audio, video, and media link statistics for both publishers and subscribers. These include packet counts, bitrates, frame rate data, pause/freeze metrics, codec information, and transport-level network metrics such as bandwidth estimation and network condition scoring.

Statistics are delivered through:

OTPublisherKitNetworkStatsDelegate — publisher-side stats (audio, video)
OTSubscriberKitNetworkStatsDelegate — subscriber-side stats (audio, video)

To receive them, enable the appropriate delegate on the publisher or subscriber.

Enabling Statistics for Publishers

Attach a class that adopts OTPublisherKitNetworkStatsDelegate:

@interface MyViewController () <OTPublisherKitDelegate, OTPublisherKitNetworkStatsDelegate>
@end

OTPublisher *publisher = [[OTPublisher alloc] initWithDelegate:self
                                                      settings:settings];
publisher.networkStatsDelegate = self;

Implement the callbacks:

- (void)publisher:(OTPublisherKit *)publisher
videoNetworkStatsUpdated:(NSArray<OTPublisherKitVideoNetworkStats *> *)statsArray {

    OTPublisherKitVideoNetworkStats *stats = statsArray.firstObject;
    if (!stats) return;

    // For routed sessions, the first element is sufficient.
    // For relayed sessions, iterate all elements if you want per-subscriber stats.
    NSString *connectionId = stats.connectionId ?: @"<none>";
    NSString *subscriberId = stats.subscriberId ?: @"<none>";

    NSLog(@"Publisher Video Stats for connectionId: %@, subscriberId: %@", connectionId, subscriberId);
    NSLog(@"Video bytes sent: %lld", stats.videoBytesSent);
    NSLog(@"Video packets sent: %lld", stats.videoPacketsSent);
    NSLog(@"Video packets lost: %lld", stats.videoPacketsLost);
    NSLog(@"Stats timestamp: %f ms", stats.timestamp);

    for (OTPublisherKitVideoLayerStats *layer in stats.videoLayers) {
        NSLog(@"Layer: %dx%d", layer.width, layer.height);
        NSLog(@"  Encoded FPS: %f", layer.encodedFrameRate);
        NSLog(@"  Bitrate: %lld bps", layer.bitrate);
        NSLog(@"  Total bitrate (incl. RTP overhead): %lld bps", layer.totalBitrate);
        NSLog(@"  Codec: %@", layer.codec ?: @"unknown");
        NSLog(@"  Scalability mode: %@", layer.scalabilityMode ?: @"none");
        NSLog(@"  Quality limitation: %@", @(layer.qualityLimitationReason));
    }
}

- (void)publisher:(OTPublisherKit *)publisher
audioNetworkStatsUpdated:(NSArray<OTPublisherKitAudioNetworkStats *> *)statsArray {

    OTPublisherKitAudioNetworkStats *stats = statsArray.firstObject;
    if (!stats) return;

    // For routed sessions, the first element is sufficient.
    // For relayed sessions, iterate all elements if you want per-subscriber stats.
    NSString *connectionId = stats.connectionId ?: @"<none>";
    NSString *subscriberId = stats.subscriberId ?: @"<none>";

    NSLog(@"Publisher Audio Stats for connectionId: %@, subscriberId: %@", connectionId, subscriberId);
    NSLog(@"Audio bytes sent: %lld", stats.audioBytesSent);
    NSLog(@"Audio packets sent: %lld", stats.audioPacketsSent);
    NSLog(@"Audio packets lost: %lld", stats.audioPacketsLost);
    NSLog(@"Stats timestamp: %f ms", stats.timestamp);
}

- (void)publisher:(OTPublisherKit *)publisher
mediaLinkStatsUpdated:(NSArray<OTPublisherKitMediaLinkStats*>*)mediaLinkStats {
    
    if (mediaLinkStats.count == 0) return;
    OTPublisherKitMediaLinkStats *stats = mediaLinkStats.firstObject;
    
    NSLog(@"Publisher uplink bandwidth: %lld bps", stats.transport.connectionEstimatedBandwidth);
    NSLog(@"Network condition: %ld", (long)stats.transport.networkCondition);
    NSLog(@"Condition reason: %ld", (long)stats.transport.networkConditionReason);
}

For a publisher in a routed session (one that uses the Vonage Video Media Router), the stats array includes one object, defining the statistics for the single audio or video media stream that is sent to the Vonage Video Media Router. In a relayed session, the stats array includes an object for each subscriber to the published stream.

Receiving Video Quality Events on the Publishers

If you are also interested in video quality events implement this callback:

- (void)publisher:(OTPublisherKit *)publisher
videoQualityChanged:(OTPublisherKitVideoNetworkStats *)stats
           reason:(OTPublisherVideoEventReason)reason {

    NSLog(@"Publisher video quality event: %ld", (long)reason);
}

Receiving Network Condition Events on the Publishers

To receive network condition change events for the publisher, implement the publisher:networkConditionChanged:mediaLinkStats:reason: callback:

- (void)publisher:(OTPublisherKit *)publisher
networkConditionChanged:(OTPublisherKitMediaLinkStats *)mediaLinkStats
             reason:(OTNetworkReason)reason {

    NSLog(@"Publisher network condition changed: %ld", (long)mediaLinkStats.transport.networkCondition);
    NSLog(@"Reason: %ld", (long)mediaLinkStats.transport.networkConditionReason);
}

This callback is triggered when a significant change in network condition is detected for the publisher. It includes the current media link statistics with transport metrics. See Network condition and degradation source for details on interpreting network condition scores and reasons.

Enabling Statistics for Subscribers

Attach a class that adopts OTSubscriberKitNetworkStatsDelegate:

@interface MyViewController () <OTSubscriberKitDelegate, OTSubscriberKitNetworkStatsDelegate>
@end

OTSubscriber *subscriber = [[OTSubscriber alloc] initWithStream:stream
                                                       delegate:self];
subscriber.networkStatsDelegate = self;
[session subscribe:subscriber error:nil];

Implement the callbacks:

- (void)subscriber:(OTSubscriberKit *)subscriber
videoNetworkStatsUpdated:(OTSubscriberKitVideoNetworkStats *)stats {
    NSLog(@"Video bytes received: %llu", stats.videoBytesReceived);
}

- (void)subscriber:(OTSubscriberKit *)subscriber
audioNetworkStatsUpdated:(OTSubscriberKitAudioNetworkStats *)stats {
    NSLog(@"Audio packets received: %llu", stats.audioPacketsReceived);
}

- (void)subscriber:(OTSubscriberKit *)subscriber
mediaLinkStatsUpdated:(OTSubscriberKitMediaLinkStats *)mediaLinkStats {
    
    NSLog(@"Local downlink bandwidth: %lld bps", mediaLinkStats.transport.connectionEstimatedBandwidth);
    NSLog(@"Remote publisher uplink bandwidth: %lld bps", mediaLinkStats.remotePublisherTransport.connectionEstimatedBandwidth);
    NSLog(@"Degradation source: %ld", (long)mediaLinkStats.networkDegradationSource);
}

Receiving Video Quality Events on the Subscribers

Additionally handle subscriber video quality changed events:

- (void)subscriber:(OTSubscriberKit *)subscriber
videoQualityChanged:(OTSubscriberKitVideoNetworkStats *)stats
            reason:(OTSubscriberVideoEventReason)reason {

    NSLog(@"Subscriber video quality event: %ld", (long)reason);
}

Receiving Network Condition Events on the Subscribers

To receive network condition change events for the subscriber, implement the subscriber:networkConditionChanged:mediaLinkStats:reason: callback:

- (void)subscriber:(OTSubscriberKit *)subscriber
networkConditionChanged:(OTSubscriberKitMediaLinkStats *)mediaLinkStats
             reason:(OTNetworkReason)reason {

    NSLog(@"Local network condition: %ld", (long)mediaLinkStats.transport.networkCondition);
    NSLog(@"Remote publisher network condition: %ld", (long)mediaLinkStats.remotePublisherTransport.networkCondition);
    NSLog(@"Degradation source: %ld", (long)mediaLinkStats.networkDegradationSource);
}

This callback is triggered when a significant change in network condition is detected for the subscriber or the remote publisher. It includes the current media link statistics with local and remote transport metrics and degradation source. See Network condition and degradation source for details on interpreting network condition scores and reasons.

Statistics Data Structures

This section outlines the structs and properties provided by the iOS audio and video statistics API. While all Video SDK platforms expose the same set of statistics, there may be minor differences in how each platform structures or names individual fields. These variations reflect platform-specific SDK design conventions rather than differences in the underlying metrics.

`OTTransportStats`

Represents shared transport-level metrics.

connectionEstimatedBandwidth – Estimated available connection bandwidth (bps).
networkCondition – Current network condition score (OTNetworkConditionUnknown, OTNetworkConditionCritical, OTNetworkConditionWarning, OTNetworkConditionFair, OTNetworkConditionGood, or OTNetworkConditionExcellent).
networkConditionReason – Primary reason impacting the network condition (OTNetworkReasonNone, OTNetworkReasonUnknown, OTNetworkReasonBandwidth, or OTNetworkReasonPacketLoss).

`OTPublisherKitVideoNetworkStats`

Provides statistics about a publisher’s video track. It includes:

connectionId – In a relayed session, the connection ID of the client subscribing to the stream. Undefined in a routed session.
subscriberId – In a relayed session, the subscribed ID of the client subscribing to the stream. Undefined in a routed session.
videoPacketsLost – Estimated video packets lost.
videoPacketsSent – Video packets sent.
videoBytesSent – Video bytes sent.
timestamp – Unix timestamp in milliseconds when stats were gathered.
startTime – The timestamp, in milliseconds since the Unix epoch, from which the cumulative totals started accumulating.
videoLayers – The array of video layer statistics (see OTPublisherKitVideoLayerStats).

`OTPublisherKitAudioNetworkStats`

Provides statistics about a publisher’s audio track. It includes:

connectionId – In a relayed session, the connection ID of the client subscribing to the stream. Undefined in a routed session.
subscriberId – In a relayed session, the subscribed ID of the client subscribing to the stream. Undefined in a routed session.
audioPacketsLost – Estimated packets lost.
audioPacketsSent – Audio packets sent.
audioBytesSent – Audio bytes sent.
timestamp – Unix timestamp in milliseconds.
startTime – The timestamp, in milliseconds since the Unix epoch, from which the cumulative totals started accumulating.
transport – Tranport level network statistics.

`OTPublisherKitVideoLayerStats`

Represents one simulcast layer or SVC layer.

width – Encoded frame width.
height – Encoded frame height.
encodedFrameRate – Encoded frames per second.
bitrate – Layer bitrate (bps).
totalBitrate – Layer bitrate including RTP overhead (bps).
scalabilityMode – SVC/scalability descriptor (e.g., "L3T3").
qualityLimitationReason – Reason for quality limitation (bandwidth, CPU, codec, resolution, or layer change).
codec – The codec used by this video layer.

`OTSenderStats`

Sender-side estimation metrics (mirrored on both audio and video).

connectionMaxAllocatedBitrate – Maximum bitrate estimated for the sender connection.
connectionEstimatedBandwidth – Current bandwidth estimation (bps).

`OTSubscriberKitVideoNetworkStats`

Provides statistics about a subscriber’s video track. It includes:

videoPacketsLost – Estimated video packets lost.
videoPacketsReceived – Video packets received.
videoBytesReceived – Video bytes received.
timestamp – Unix timestamp in milliseconds when stats were gathered.
senderStats – Sender-side metrics (optional).
width – Decoded frame width in pixels.
height – Decoded frame height in pixels.
decodedFrameRate – Decoded frames per second.
bitrate – Video bitrate (bps).
totalBitrate – Bitrate including RTP overhead (bps).
pauseCount – Number of pauses (>5s since last frame). Includes intentional disables and audio-fallback cases.
totalPausesDuration – Total pause duration (ms).
freezeCount – Freeze count (WebRTC-defined freeze event).
totalFreezesDuration – Total freeze duration (ms).
codec – Current decoder codec.

`OTSubscriberKitAudioNetworkStats`

Provides statistics about a subscriber's audio track. It includes:

audioPacketsLost – Estimated packets lost.
audioPacketsReceived – Packets received.
audioBytesReceived – Bytes received.
timestamp – Unix timestamp in milliseconds.
senderStats – Sender-side metrics (optional).

`OTPublisherKitMediaLinkStats`

Provides transport-level statistics for a publisher's connection.

transport – Transport statistics for this publisher (see OTTransportStats)

`OTSubscriberKitMediaLinkStats`

Provides transport-level statistics for a subscriber's connections, including visibility into the remote publisher's network performance. This enables applications to diagnose whether connection issues originate from the subscriber's downlink or the publisher's uplink.

transport – Transport statistics for this subscriber's downlink connection (see OTTransportStats)
remotePublisherTransport – Transport statistics for the remote publisher's uplink connection (obtained via sender-side statistics, see OTTransportStats). These stats may be limited if sender-side statistics are not enabled.
networkDegradationSource – Indicates the source of network degradation (OTNetworkDegradationSourceLocal, OTNetworkDegradationSourceRemote, OTNetworkDegradationSourceBothOrUnclear, or OTNetworkDegradationSourceUnknown)

Sender-Side statistics

See the sender-side statistics overview.

Enabling Sender-Side Statistics

Sender-side statistics are received on the subscribers. To receive sender-side statistics, enable them for the stream’s publisher by setting the senderStatsTrack property to true for the OTPublisherKitSettings object used to create the publisher.

OTPublisherKitSettings *settings = [[OTPublisherKitSettings alloc] init];
settings.senderStatsTrack = YES;

OTPublisher *publisher = [[OTPublisher alloc] initWithDelegate:self
                                                      settings:settings];

If senderStatsTrack is not enabled, no sender statistics channel will be published for this publisher. The default value is NO.

Subscribing to Sender-Side Statistics

If the stream’s publisher has enabled sender-side statistics, subscribers start receiving them automatically once a listener is registered for video or audio stats, as described above.

Implement the delegate method for video stats:

- (void)subscriber:(OTSubscriberKit *)subscriber
videoNetworkStatsUpdated:(OTSubscriberKitVideoNetworkStats *)stats
{
    // The property may be nil if no sender statistics have been received yet.
    if (stats.senderStats) {
        OTSenderStats *sender = stats.senderStats;
        NSLog(@"Connection max allocated bitrate: %lld bps", (long long)sender.connectionMaxAllocatedBitrate);
        NSLog(@"Connection current estimated bandwidth: %lld bps", (long long)sender.connectionEstimatedBandwidth);
    } else {
        NSLog(@"Sender-side stats not available yet.");
    }
}

Similarly implement -subscriber:audioNetworkStatsUpdated: for audio stats, which also includes a senderStats property.

Receiving Statistics Events

Sender-side statistics are delivered via the OTSubscriberKitNetworkStatsDelegate callbacks for video and audio, as shown above. The OTSenderStats, included as the senderStats member in both OTSubscriberKitVideoNetworkStats and OTSubscriberKitAudioNetworkStats, provides two properties:

connectionMaxAllocatedBitrate — The maximum bitrate that can be estimated for the connection
connectionEstimatedBandwidth — The current estimated bandwidth for the connection

These two metrics are calculated per audio-video bundle, so the same values appear in both video and audio statistics. Because they reflect the transport rather than individual tracks, the metrics are shared across both audio and video.

Network condition and degradation source

The SDK provides real-time network condition metrics for both publishers and subscribers, including a condition score, the reason driving that score, and a degradation source for subscribers. For a full explanation of the network condition model, scores, reasons, and how to enable it, see the client observability overview.

Network condition data is available through two channels:

Periodic statistics: The media link stats events include transport metrics with networkCondition and networkConditionReason. For subscribers, media link stats also include remotePublisherTransport and networkDegradationSource.
Network condition changed events: Dedicated callbacks on both publisher and subscriber are triggered when a significant change in network condition is detected.

The following example shows how to use the subscriber network condition data to identify the source of degradation:

- (void)subscriber:(OTSubscriberKit *)subscriber
networkConditionChanged:(OTSubscriberKitMediaLinkStats *)mediaLinkStats
             reason:(OTNetworkReason)reason {

    OTNetworkCondition localCondition = mediaLinkStats.transport.networkCondition;
    OTNetworkCondition remoteCondition = mediaLinkStats.remotePublisherTransport.networkCondition;
    OTNetworkDegradationSource source = mediaLinkStats.networkDegradationSource;

    if (source == OTNetworkDegradationSourceLocal) {
        NSLog(@"Local network is degraded (condition: %ld)", (long)localCondition);
    } else if (source == OTNetworkDegradationSourceRemote) {
        NSLog(@"Remote publisher network is degraded (condition: %ld)", (long)remoteCondition);
    } else if (source == OTNetworkDegradationSourceBothOrUnclear) {
        NSLog(@"Degradation source unclear — local: %ld, remote: %ld", (long)localCondition, (long)remoteCondition);
    }
}

RTC Stats Report

To get publisher low-level peer connection statistics, use the [OTPublisherKit getRtcStatsReport:] method. This provides RTC stats reports for the media stream.

This is an asynchronous operation. Set the >[OTPublisherKit rtcStatsReportDelegate]> property and implement the >[OTPublisherKitRtcStatsReportDelegate publisher:rtcStatsReport:]> method prior to calling [OTPublisherKit getRtcStatsReport:].

When the stats are available, the implementation of the >[OTPublisherKitRtcStatsReportDelegate publisher:rtcStatsReport:]> message is sent. The message includes an array of OTPublisherRtcStats objects, which includes a jsonArrayOfReports property.

This is a JSON array of RTC stats reports, which are similar to the format the RtcStatsReport object implemented in web browsers (see these Mozilla docs).

To get subscriber low-level peer connection statistics, use the [OTSubscriberKit getRtcStatsReport:] method. This provides an RTC stats report for the media stream.

This is an asynchronous operation. Set the [OTSubscriberKit rtcStatsReportDelegate]> property and implement the >[OTSubscriberKitRtcStatsReportDelegate subscriber:rtcStatsReport:]> method prior to calling [OTSubscriberKit getRtcStatsReport:].

When the stats are available, the implementation of the >[OTSubscriberKitRtcStatsReportDelegate subscriber:rtcStatsReport:]> message is sent. The message includes an a jsonArrayOfReports parameter.

This is a JSON array of RTC stats reports, which are similar to the format the RtcStatsReport object implemented in web browsers (see these Mozilla docs).

Also see this W3C documentation.

Sample

The Vonage Video iOS SDK Client Observability Sample App demonstrates client observability features in a mobile app built with the iOS client SDK.

Navigation

Client Observability: iOS

Audio, Video and Media Link Statistics API

Enabling Statistics for Publishers

Receiving Video Quality Events on the Publishers

Receiving Network Condition Events on the Publishers

Enabling Statistics for Subscribers

Receiving Video Quality Events on the Subscribers

Receiving Network Condition Events on the Subscribers

Statistics Data Structures

OTTransportStats

OTPublisherKitVideoNetworkStats

OTPublisherKitAudioNetworkStats

OTPublisherKitVideoLayerStats

OTSenderStats

OTSubscriberKitVideoNetworkStats

OTSubscriberKitAudioNetworkStats

OTPublisherKitMediaLinkStats

OTSubscriberKitMediaLinkStats