HaishinKit.swift/RTCHaishinKit/Sources/RTP/RTPTimestamp.swift

import AVFAudio
import CoreMedia
import Foundation

struct RTPTimestamp {
    static let startedAt: Double = -1

    private let rate: Double
    private var startedAt = Self.startedAt

    init(_ rate: Double) {
        self.rate = rate
    }

    func convert(_ timestamp: UInt32) -> AVAudioTime {
        return AVAudioTime(hostTime: AVAudioTime.hostTime(forSeconds: Double(timestamp) / rate))
    }

    func convert(_ timestamp: UInt32) -> CMTime {
        return CMTime(value: CMTimeValue(timestamp), timescale: CMTimeScale(rate))
    }

    mutating func convert(_ when: AVAudioTime) -> UInt32 {
        let seconds: Double
        if when.hostTime != 0 {
            seconds = AVAudioTime.seconds(forHostTime: when.hostTime)
        } else {
            seconds = Double(when.sampleTime) / when.sampleRate
        }
        if startedAt == Self.startedAt {
            startedAt = seconds
        }
        let timestamp = UInt64((seconds - startedAt) * rate)
        return UInt32(timestamp & 0xFFFFFFFF)
    }

    mutating func convert(_ time: CMTime) -> UInt32 {
        let seconds = time.seconds
        if startedAt == Self.startedAt {
            startedAt = seconds
        }
        let timestamp = UInt64((seconds - startedAt) * rate)
        return UInt32(timestamp & 0xFFFFFFFF)
    }

    mutating func reset() {
        startedAt = Self.startedAt
    }
}