ImageDecoder-frameDuration.swift

func frameDuration(at index: Int) -> TimeInterval? {
    guard let frameProperties = CGImageSourceCopyPropertiesAtIndex(imageSource, index, imageSourceOptions()) as? [CFString: Any] else {
        return nil
    }

    var animationProperties = ImageDecoder.animationProperties(from: frameProperties)

    if animationProperties == nil {
        if let properties = CGImageSourceCopyProperties(imageSource, imageSourceOptions()) as? [CFString: Any] {
            animationProperties = ImageDecoder.animationHEICSProperties(from: properties, at: index)
        }
    }

    let duration: TimeInterval

    // Use the unclamped frame delay if it exists. Otherwise use the clamped frame delay.
    if let unclampedDelay = animationProperties?["UnclampedDelayTime" as CFString] as? TimeInterval {
        duration = unclampedDelay
    }
    else if let delay = animationProperties?["DelayTime" as CFString] as? TimeInterval {
        duration = delay
    }
    else {
        duration = 0.0
    }

    // WebCore won't allow frame duration faster than 10ms.
    return duration < 0.011 ? 0.1 : duration
}