ADOFAIRenderer/Util/Audio/AudioSyncCalculator.cs

using System;

namespace ADOFAIRenderer.Util.Audio
{
    internal class AudioSyncCalculator
    {
        private readonly long _sampleRate;
        private readonly (long Numerator, long Denominator) _fpsRational;

        // ReSharper disable once NotAccessedField.Local
        private long _currentSample;
        private long _remainder;
        
        public AudioSyncCalculator(long sampleRate, double fps)
        {
            _sampleRate = sampleRate;
            _fpsRational = RationalUtil.Double2MaxPrecisionInt(fps);

            // NTSC
            if (Math.Abs(fps - 29.97) < 0.001) _fpsRational = (30000, 1001);
            if (Math.Abs(fps - 59.94) < 0.001) _fpsRational = (60000, 1001);
            if (Math.Abs(fps - 23.976) < 0.001 || Math.Abs(fps - 23.98) < 0.001) _fpsRational = (24000, 1001);
        }

        public void Reset()
        {
            _currentSample = 0;
            _remainder = 0;
        }

        public int GetNextFrameSamples()
        {
            var numerator = _sampleRate * _fpsRational.Denominator + _remainder;
            var samplesNeeded = numerator / _fpsRational.Numerator;

            _remainder = numerator % _fpsRational.Numerator;
            _currentSample += samplesNeeded;
            return (int)samplesNeeded;
        }
    }
}