Add frequency resampler & use it in mp3 decoder

libs/audio/include/psemek/audio/resampler.hpp

@@ -0,0 +1,30 @@
+#pragma once
+
+#include <psemek/util/span.hpp>
+
+#include <vector>
+
+namespace psemek::audio
+{
+
+	struct resampler
+	{
+		// ratio is target frequency / source frequency
+		void feed(util::span<float const> samples, float ratio);
+
+		util::span<float const> result() const
+		{
+			return result_;
+		}
+
+	private:
+		std::vector<float> result_;
+		int position_{0};
+		float position_frac_{0.f};
+
+		float last_sample_[2] {0.f, 0.f};
+
+		void advance(float delta);
+	};
+
+}

libs/audio/source/resampler.cpp

@@ -0,0 +1,46 @@
+#include <psemek/audio/resampler.hpp>
+#include <psemek/geom/math.hpp>
+
+#include <vector>
+
+namespace psemek::audio
+{
+
+	void resampler::feed(util::span<float const> samples, float ratio)
+	{
+		result_.clear();
+
+		if (samples.empty())
+			return;
+
+		float const delta = 1.f / ratio;
+
+		while (position_ < 0)
+		{
+			result_.push_back(geom::lerp(last_sample_[0], samples[0], position_frac_));
+			result_.push_back(geom::lerp(last_sample_[1], samples[1], position_frac_));
+			advance(delta);
+		}
+
+		while (2 * position_ + 3 < samples.size())
+		{
+			result_.push_back(geom::lerp(samples[2 * position_ + 0], samples[2 * position_ + 2], position_frac_));
+			result_.push_back(geom::lerp(samples[2 * position_ + 1], samples[2 * position_ + 3], position_frac_));
+			advance(delta);
+		}
+
+		position_ -= static_cast<int>(samples.size()) / 2;
+
+		last_sample_[0] = samples[samples.size() - 2];
+		last_sample_[1] = samples[samples.size() - 1];
+	}
+
+	void resampler::advance(float delta)
+	{
+		position_frac_ += delta;
+		auto floor = static_cast<int>(std::floor(position_frac_));
+		position_ += floor;
+		position_frac_ -= floor;
+	}
+
+}

libs/audio/source/track_mp3.cpp

@@ -1,4 +1,6 @@
 #include <psemek/audio/track.hpp>
+#include <psemek/audio/resampler.hpp>
+#include <psemek/audio/constants.hpp>
 
 #include <psemek/audio/minimp3/options.h>
 #include <psemek/audio/minimp3/minimp3.h>
@@ -31,7 +33,7 @@ namespace psemek::audio
 		{
 			mp3_stream_impl(std::shared_ptr<mp3_data_holder> data)
 				: data_(std::move(data))
-				, buffer_(MINIMP3_MAX_SAMPLES_PER_FRAME)
+				, source_buffer_(MINIMP3_MAX_SAMPLES_PER_FRAME)
 			{
 				mp3dec_init(&decoder_);
 			}
@@ -48,33 +50,35 @@ namespace psemek::audio
 				std::size_t result = 0;
 				while (result < sample_count)
 				{
-					if (buffer_pos_ < buffer_size_)
+					if (resampler_pos_ < resampler_.result().size())
 					{
-						std::size_t size = std::min(buffer_size_ - buffer_pos_, sample_count - result);
+						std::size_t size = std::min(resampler_.result().size() - resampler_pos_, sample_count - result);
-						std::copy(buffer_.data() + buffer_pos_, buffer_.data() + buffer_pos_ + size, data + result);
+						std::copy(resampler_.result().data() + resampler_pos_, resampler_.result().data() + resampler_pos_ + size, data + result);
-						buffer_pos_ += size;
+						resampler_pos_ += size;
 						result += size;
 					}
 					else
 					{
 						mp3dec_frame_info_t frame_info;
-						buffer_size_ = mp3dec_decode_frame(&decoder_, input + read_bytes_, data_->data.size() - read_bytes_, buffer_.data(), &frame_info);
+						auto source_buffer_size = mp3dec_decode_frame(&decoder_, input + read_bytes_, data_->data.size() - read_bytes_, source_buffer_.data(), &frame_info);
-						buffer_pos_ = 0;
+						resampler_pos_ = 0;
 						read_bytes_ += frame_info.frame_bytes;
 
-						if (frame_info.channels == 1)
-						{
-							for (std::size_t i = buffer_size_ * 2; i > 0;)
-							{
-								i -= 2;
-								buffer_[i + 0] = buffer_[i / 2];
-								buffer_[i + 1] = buffer_[i / 2];
-							}
-							buffer_size_ *= 2;
-						}
-
 						if (frame_info.frame_bytes == 0)
 							break;
+
+						if (frame_info.channels == 1)
+						{
+							for (std::size_t i = source_buffer_size * 2; i > 0;)
+							{
+								i -= 2;
+								source_buffer_[i + 0] = source_buffer_[i / 2];
+								source_buffer_[i + 1] = source_buffer_[i / 2];
+							}
+							source_buffer_size *= 2;
+						}
+
+						resampler_.feed({source_buffer_.data(), source_buffer_.data() + source_buffer_size}, static_cast<float>(frequency) / frame_info.hz);
 					}
 				}
 
@@ -91,9 +95,11 @@ namespace psemek::audio
 			std::size_t read_bytes_{0};
 
 			mp3dec_t decoder_;
-			std::vector<float> buffer_;
+			std::vector<float> source_buffer_;
-			std::size_t buffer_pos_{0};
+
-			std::size_t buffer_size_{0};
+			resampler resampler_;
+			std::size_t resampler_pos_{0};
+
 			std::atomic<std::size_t> played_{0};
 		};