Session Replay

As session collection will start at the 1st screenview event, it is required to have screen tracking implemented. Make sure to follow the Track screens section.

Updating to latest SDK version

Section titled Updating to latest SDK version

In order to enable Session Replay in your app and get the most stable version, it is required to upgrade the SDK to its latest version.

If you are in the process of implementing the SDK for the 1st time (or choose to take this update as an opportunity to review your Privacy related implementation), make sure to follow the Privacy section.

WebView events can be collected as part of the Session Replay under the following conditions:

  • The app is a native iOS app (other platforms coming soon including React Native, etc.)
  • The WebView is registered to the SDK
  • The web page implements the Web Tracking Tag

For the full guide to implementation of Webview Tracking, see 📚 Mobile Apps Webview Tracking.

WebView personal data masking is entirely handled on the web side — see 📚 Personal Data handling in WebView.

Enable Session Replay on your device

Section titled Enable Session Replay on your device

Since not all sessions are collected (depending on the percentage set in Contentsquare back-office), we have implemented an option to force replay collection on your device for testing and debugging purpose. This option can be enabled from the in-app features settings:

  1. Enable in-app features
  2. Open in-app features settings with a long press on the snapshot button
  3. In the “Session replay settings” section, enable session Replay
  4. Kill the app
  5. Start app, a new session is starting with Session Replay enabled

How do I know if Session Replay is enabled?

Section titled How do I know if Session Replay is enabled?

There are 2 places where you can check if Session Replay is enabled:

In the logs: The log Session Recording is starting will confirm that Session Replay is enabled.

In in-app features settings: Below the “Enable “will start at next app start” (see below Access the replay), you will either see:

  • No replay link available which means Session Replay is not running for the current session
  • Get Replay link which means Session Replay is running for the current session

The session can be accessed by tapping on Get replay link button from the in-app features settings:

The replay will be available within 5 minutes. Only the “ended screen views” are processed (we know a screenview is ended when we start receiving data for the next screenview). This means that you will be able to replay your session up to the previous screenview if the session is still running.

Since texts are collected as data for UIKit elements, it is required to get the custom fonts you use in your app so the player can properly render the texts as displayed in your app.

You can manage custom fonts directly from the player as explained in this article Managing iOS Fonts In The Player

The Session Replay feature replays every interaction of your users with your app. In order to respect the user’s right to privacy, the Contentsquare SDK :

  • Masks everything by default
  • Allows you to control which part of the user interface is collected via our masking and un-masking APIs.

Masking depends on the type of element:

  • UIKit.UIImage and SwiftUI.Image: image isn’t collected, a placeholder is sent instead of the content; the “IMG” placeholder will be displayed in the frame of the element.
  • UIKit.UILabel and UIKit.UITextView: text is replaced by “la” repeated as many times as needed to equal the original character count. White characters are preserved. For instance the lazy fox is collected as lal lala ala. All other visual properties are collected (text color, background color, alignment, etc.).
  • UIKit.UITextField: same as UIKit.UILabel or UIKit.UITextView unless isSecureTextEntry is set to true. In this case all characters, including whitespaces are replaced with ”•“.
  • SwiftUI.Text: element is replaced by a black rectangle.
  • For all other types: no specific data is collected but all visual properties are collected: size, background color, corner radius, etc.

If you think a specific element can reveal personal data from one of these properties you have to mask it using one of the method presented below. A good way to check how a view is rendered in the Session Replay is to navigate to the desired view with the CS SDK running then use the quick replay link.

Original VS Replay fully masked

Section titled Original VS Replay fully masked

All iOS views and subclasses of UIView are fully masked by default. The SDK provides a simple API to change the default masking state:

/// Change the masking state of all types of views.
/// - Parameter mask: true restores the default masking state.
/// false unmasks every types of views.
static func setDefaultMasking(_ mask: Bool)

Masking/Un-masking by instances

Section titled Masking/Un-masking by instances

Use mask(view:) and unmask(view:) methods to deal with a specific instance. Masking is applied recursively to all subviews unless specified otherwise (cf. Masking and Unmasking behaviors on a parent view).

Following the previous example on un-masking UIButtons: you are in default masking, the UIButton are unmasked but a screen shows a button, myButton, that contains sensitive information. You will be able to mask it with mask(view: myButton).

The Contentsquare SDK allows masking elements by type for convenience but it isn’t the recommended masking mechanism because it will impact all screens of your application. For instance, it can be useful in the case where you have a specific class for presenting user information or for displaying the user profile picture to make sure it always stays mask.

Use mask(viewsOfType:) and unmask(viewsOfType:) methods if you want to handle a specific type (wether being a system element or a custom element).

Example: un-masking UIButtons If you are in default masking but you don’t want any button to be masked, you will only need to call unmask(viewsOfType: UIButton.self): to specify that all instances of UIButton and its subclasses should not be masked.

The SDK determines if a view is masked or not by applying the above rules in the following order. Once a rule is triggered, the state is set (subsequent rules won’t be applied):

1Instance is specifically masked or unmasked
2A parent is specifically masked or unmasked
3Type is masked or unmasked
4A parent type is masked or unmasked
5Otherwise the default masking state is applied

Masking and Unmasking behaviors on a parent view

Section titled Masking and Unmasking behaviors on a parent view

Masking is applied recursively to all children unless a specific rule has been applied to 1 of them. In this case the rule will again be applied recursively.


Let’s say we have the following structure:

(parent view)
| "Parent Label" |
| |
| (child view) |
| -------------------- |
| | "Child Label" | |
| | | |
| -------------------- |
| |
  • If no rule is applied: everything is masked including “Parent Label” and “Child Label”
  • If parent view is unmasked and no other rule is applied: both “Parent Label” and “Child Label” are unmasked
  • If parent view is unmasked and child view is masked: “Parent Label” is unmasked and “Child Label” is masked
  • If default masking is set to false and no other rule is applied: “Parent Label” and “Child Label” are unmasked
  • If default masking is set to false and parent view is masked: both “Parent Label” and “Child Label” are masked

And so on as explained in the Masking rules priority.

Unmask an instance when its type is masked If you’ve masked UILabel types specifically or are in default masking, and you call unmask(view: myLabel), all UILabel instances will be masked except myLabel.

Mask an instance when its type is unmasked If you’ve unmasked UILabel type specifically or are using the default masking, and you call mask(view: myLabel), no UILabel will be masked except myLabel.

Implementation recommendations

Section titled Implementation recommendations

Masking operations should always be performed before the target view is added to the window to avoid any Personal Data leak. For instance, you can set up masking in the didFinishLaunching callback of your app or if you need to change masking behavior while your app is launched, it can be done in loadView, viewDidLoad or viewWillAppear if you use a ViewController.

Keeping track of what is masked

Section titled Keeping track of what is masked

The SDK doesn’t provide a list of what is currently masked, if you need to keep track, you probably will have to write your specific wrapper.

Masking operations performance impact

Section titled Masking operations performance impact

Repeating the same operation has little to no impact, e.g you can call unmask(viewsOfType: UIButton.self) multiple times without impacting the SDK or your app performances.

Contentsquare provides the ability to search for session(s) associated with a specific visitor, based on an identifier: email, phone number, customer ID… As these values are typically Personal Identifiable Information, from the moment the SDK is collecting the User Identifier, we immediately encode the value using a hashing algorithm so that the information is hidden and can never be accessed.

Use the following code to send a user identifier:


When called, the SDK will log:

CSLIB ℹ️ Info: User identifier hashed sent {value}

Sending a user identifier for each session

Section titled Sending a user identifier for each session

You may want to send the user identifier for each session. While triggering the user identifier at app launch will cover most cases, it will not be enough. A session can start when the app is put in foreground, after staying in background for more than 30 minutes. See Session definition section for more information.

That is why we also recommend sending the user identifier every time the app enters foreground.

You can use didBecomeActiveNotification notification and sceneDidBecomeActive(_:) callback to detect foreground and trigger a sendUserIdentifier().

  • User identifier max length is 100 characters (if the limit is exceeded, the user identifier will not be handled and you will see an error message in the Console/Logcat)
  • Only the first 15 user identifiers per view will be processed on server side
  • The SDK will trim and lowercase user identifier
  • User identifier event are not visible in Log visualizer

Contentsquare provides the ability to retrieve the link to the session replay to be attached to other vendors such as Voice of customers tools, Crash reporting tools.

Section titled Get current Session Replay Link

Generate a link to the replay of the current session. This link can be pushed to any internal or 3rd-party tool as a custom property/variable. For instance, you can add the replay link to:

  • Each user request sent to your customer service tool
  • Each user voting in your Voice of Customer tool
  • Each user session in your App Performance, Observability tool

You can register to replay link creation and updates using the following API:

Contentsquare.onSessionReplayLinkChange { link in
self.currentCSReplayLink = link

When you call this API, the SDK logs:

CSLIB ℹ️ Info: Callback for SessionReplay link update is registered.

To unregister the current callback, simply pass nil as the argument:


When you call this API, the SDK logs:

CSLIB ℹ️ Info: Callback for SessionReplay link update is unregistered.

When a new link is available, the SDK logs:

CSLIB ℹ️ Info: SessionReplay link updated:{projectId}&uu={userId}&sn={sessionNumber}&recordingType=cs

If you have a Contentsquare account, you can use this link to directly watch your current session replay on the Contentsquare Platform.

The replay will be available within 5 minutes. Only the “ended screen views” are processed (we know a screenview is ended when we start receiving data for the next screenview). This means that you will be able to replay the session up to the previous screenview if the session is still running.

Sessions can be collected for Session Replay if the Session Replay feature has been enabled for your project and the session matches the collection criteria.

The following conditions will have an impact on which sessions will be collected:

  • User consent: The users have given their consent (if required)
  • Collection rate: The session is being drawn for collection (see Collection Rate below)
  • Compatibility: The OS version is supported.
  • App version: The app version is not part of the block list (see App version block list below)

Note that, when Session Replay is turned off, no content specific to Session Replay is collected whatsoever. Also note that the standard Contentsquare analytics tracking remain unaffected by this.

Session Replay collection is based on a percentage of the total sessions. By default Session Replay collection is disabled.

During the early access phase, the percentage or collected sessions will be set to 1% at the beginning. It will then be adjusted according to:

  • The traffic on your app
  • The volume of collected sessions set in the contract

See Compatibility.

Contentsquare team can add versions of your app in the block list to make sure Session Replay does not start on these versions. This can be useful when a problem is discovered on a specific version of your app, such as a Personal Data for which the masking was forgotten. This allows to keep Session Replay working on the other app versions (especially the new ones with the fix).

The SDK monitors the application lifecycle events and the view hierarchy, and generates session replay data from the behavior of the app, the content of the screen and the interaction of the user. These events are then locally stored, and eventually sent to our servers in batches. We then aggregate that data to create usable visual information into our Web Application, which you use to gather insights.

Session Replay has three quality levels available: High, Medium, Low. Quality level is defined by the frame rate and the image quality. The quality level is defined independently for Wi-Fi and Cellular Network. The default level for both is Medium. For more information on network data consumption see: Performance Impact section.

Select the image to open the it in full size and GIF format.

By default, Session Replay data can be sent over cellular network. If the particular context of your app and/or users requires a very limited impact on cellular data consumption, sending data over cellular network can be completely disabled. Once disabled, data will be sent when the device is using Wi-Fi.

Reach out to your Contentsquare contact that will make the adjustment in the project configuration.

Before being sent, data is stored in local files on disk up to 30MB on iOS and 20MB on Android. If the limit is reached, Session Replay is stopped. It will restart at the next app launch once the SDK is able to send the data.

The maximum request size is 1Mbyte.

Requests are sent:

We always strive to be non-intrusive, and transparent to the developers of the client app. We apply this rule on the performance as well. These are the technical specifics we can share on performance, if you have any questions feel free to reach out to us.

Most operations related to Session Collection are performed on background threads, for the impact on the main thread to be minimal. To make sure of this, we run performance tests on testing applications, using XCTMetric and Hitch Time Ratio measures.

We also set up mechanisms that stop the Session Collection if we detect the feature is using too much memory.

We defined our network strategy to have the lesser impact on CPU and battery of the users devices. We measure these impacts, using Apple Dev Tools, for each release of our SDK.

Session Collection will also stop if we use up to 30Mbytes of local storage.

You can reduce the quality level if you want to favor performance impact over quality.

The following performance results were obtained under the following conditions:

Device modeliPhone 7
iOS version15.7.8
Test App built using Xcode version14.3.1
Test App built with Swift version5.8
Quality levelHigh
Default Masking StateDisabled

We conducted the tests using a default Master-Detail app built using AdHoc distribution with no app thinning and with Swift symbols stripped. In the app, the SDK was making calls to the Public APIs, running and collection data in its default state.

Max CPU overhead<10%
Max RAM usage<5MB
Session Replay data transmitted over network during 1 minute of use
- with “High quality” level<2Mbytes
- with “Medium quality” level<1Mbytes
- with “Low quality” level<900Kbytes

Maps can potentially contain Personal Data and are therefore replaced by a placeholder with no ability to un-mask them currently.

The exported HTML doesn’t support the expansion, obliqueness, paragraphStyle and textEffect attributes.

Multi-window is not supported.

System elements like UIImagePickerController, SKStoreReviewController are not collected.

Requests are not sent from an iOS simulator

Section titled Requests are not sent from an iOS simulator

If you struggle to watch a replay collected on an emulator/simulator, it may be due to some network constraints applied on your computer (VPN, company network restrictions, etc.). Check your configuration and/or use a real device.

See Requests are failing for more information about our endpoints and requests.

Very long session on an iOS simulator

Section titled Very long session on an iOS simulator

If you leave the simulator/emulator running with the app in foreground, the session will not end, even if you are inactive. This can lead to artificially long sessions (several hours). To better emulate actual user behavior, put the app in background or kill it.

Unmasking with CS InApp features is broken

Section titled Unmasking with CS InApp features is broken

When activating the toggle in CS InApp to unmask the elements in the Session Replay, it can sometimes give a strange result with some elements still masked, it’s especially true for SwiftUI. This is due to the fact that unmasking with InApp features acts differently that when done in the code by the app developer. To ensure a session is fully unmasked as it would be if it was done in the code of the app, follow these steps:

  • Toggle the “Unmask …” switch
  • Navigate to a different screen
  • Go back to the previous screen
  • Put the app in background
  • Wait for the session timeout
  • Re-open the app From this point on, you will have a fully unmasked session.

Uncaught exception due to NSAttributedString

Section titled Uncaught exception due to NSAttributedString

If the following exception is encountered: NSInvalidArgumentException: -[__NSCFType CGColor]: unrecognized selector sent to instance,

It is probably due to an Objective-C bridging issue in Foundation, which makes it possible to pass CGColor instances as values for the foregroundColor and strikeThroughColor attributes of a NSAttributedString.

While a UILabel with such an attributed string will be displayed correctly, its textColor attribute will have the wrong type, and the SDK won’t be able to handle it, causing a crash in Session Replay.

Because of this, it is important to ensure that actual UIColor instances are passed as values, as per the official documentation.