Unreal Live Link Face Plugin: How to detect when the face is out of the camera?

Question

I’m following the Recording Facial Animation from an iPhone X tutorial with Unreal Engine 4 and capturing and presenting my face movement successfully.
But when my face is out of the camera, the pose in the editor will stuck in the last frame.
How could I detect the lost of live animation data so to play a prerecorded animation?

Answer 1

I have figured it out. Just use ILiveLinkClient::IsSubjectValid(SubjectName); method from the LiveLinkPlugin source in c++ or export it to Blueprint:

class DAZTOUE4_API UMyBlueprintFunctionLibrary : 
public UBlueprintFunctionLibrary
{
    GENERATED_BODY()

    UFUNCTION(BlueprintCallable, Category = "MyVirtualCharacter")
    static bool IsLiveLinkSubjectValid(const FLiveLinkSubjectName SubjectName);
};

bool UMyBlueprintFunctionLibrary::IsLiveLinkSubjectValid(const FLiveLinkSubjectName SubjectName)
{
    IModularFeatures& ModularFeatures = IModularFeatures::Get();
    if (ModularFeatures.IsModularFeatureAvailable(ILiveLinkClient::ModularFeatureName))
    {
        ILiveLinkClient& LiveLinkClient = ModularFeatures.GetModularFeature<ILiveLinkClient>(ILiveLinkClient::ModularFeatureName);
        return LiveLinkClient.IsSubjectValid(SubjectName);
    }
    return false;
}