Improve audio duration api

libs/audio/include/psemek/audio/constants.hpp

@@ -9,14 +9,24 @@ namespace psemek::audio
 	constexpr int frequency = 44100;
 	constexpr float inv_frequency = 1.f / frequency;
 
+	inline std::int64_t seconds_to_frames(float seconds)
+	{
+		return static_cast<std::int64_t>(std::round(seconds * frequency));
+	}
+
 	inline std::int64_t seconds_to_samples(float seconds)
 	{
-		return static_cast<std::int64_t>(2 * std::round(seconds * frequency));
+		return 2 * seconds_to_frames(seconds);
+	}
+
+	inline float frames_to_seconds(std::int64_t frames)
+	{
+		return static_cast<float>(frames) * inv_frequency;
 	}
 
 	inline float samples_to_seconds(std::int64_t samples)
 	{
-		return static_cast<float>(samples) * 0.5f * inv_frequency;
+		return frames_to_seconds(samples / 2);
 	}
 
 	inline float to_db(float amplitude)

libs/audio/include/psemek/audio/duration.hpp

@@ -10,66 +10,87 @@ namespace psemek::audio
 
 	struct duration
 	{
+	private:
+		struct samples_tag{};
+		struct frames_tag{};
+
+	public:
+
 		duration()
-			: samples_{0}
+			: frames_{0}
 		{}
 
-		duration(std::int64_t samples)
-			: samples_{samples}
-		{}
+		static duration from_samples(std::int64_t samples)
+		{
+			return duration(samples_tag{}, samples);
+		}
 
-		duration(std::size_t samples)
-			: samples_{samples}
-		{}
+		static duration from_frames(std::int64_t samples)
+		{
+			return duration(frames_tag{}, samples);
+		}
 
 		duration(float seconds)
-			: samples_{seconds_to_samples(seconds)}
+			: frames_{seconds_to_frames(seconds)}
 		{}
 
 		duration(duration const & other)
-			: samples_{other.samples_}
+			: frames_{other.frames_}
 		{}
 
 		float seconds() const
 		{
-			return samples_to_seconds(samples_);
+			return frames_to_seconds(frames_);
+		}
+
+		std::int64_t frames() const
+		{
+			return frames_;
 		}
 
 		std::int64_t samples() const
 		{
-			return samples_;
+			return frames_ * 2;
 		}
 
 		duration & operator = (duration const & other)
 		{
-			samples_ = other.samples_;
+			frames_ = other.frames_;
 			return *this;
 		}
 
 		duration & operator += (duration const & other)
 		{
-			samples_ += other.samples_;
+			frames_ += other.frames_;
 			return *this;
 		}
 
 		duration & operator -= (duration const & other)
 		{
-			samples_ -= other.samples_;
+			frames_ -= other.frames_;
 			return *this;
 		}
 
 		friend duration operator + (duration const & d1, duration const & d2)
 		{
-			return duration{d1.samples() + d2.samples()};
+			return duration{d1.frames() + d2.frames()};
 		}
 
 		friend duration operator - (duration const & d1, duration const & d2)
 		{
-			return duration{d1.samples() - d2.samples()};
+			return duration{d1.frames() - d2.frames()};
 		}
 
 	private:
-		std::int64_t samples_;
+		std::int64_t frames_;
+
+		duration(samples_tag, std::int64_t samples)
+			: frames_(samples / 2)
+		{}
+
+		duration(frames_tag, std::int64_t frames)
+			: frames_(frames)
+		{}
 	};
 
 }

libs/audio/source/effect/fade_out.cpp

@@ -38,7 +38,7 @@ namespace psemek::audio
 
 				if (result <= start_.samples())
 				{
-					start_ -= result;
+					start_ -= duration::from_samples(result);
 				}
 				else
 				{