Implement audio sync foundations

app/audio/audiowaveformsync.cpp

@@ -0,0 +1,152 @@
+/***
+
+  Oak - Non-Linear Video Editor
+  Copyright (C) 2026 Oak Team
+
+  This program is free software: you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation, either version 3 of the License, or
+  (at your option) any later version.
+
+  This program is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+***/
+
+#include "audiowaveformsync.h"
+
+#include <algorithm>
+#include <cmath>
+
+namespace olive
+{
+
+QVector<double>
+AudioWaveformSync::ExtractRmsEnvelope(const core::SampleBuffer &samples,
+									  size_t window_samples)
+{
+	QVector<double> envelope;
+
+	const int channel_count = samples.channel_count();
+	const size_t sample_count = samples.sample_count();
+	if (!channel_count || !sample_count || !window_samples) {
+		return envelope;
+	}
+
+	const size_t window_count =
+		(sample_count + window_samples - 1) / window_samples;
+	envelope.resize(static_cast<int>(window_count));
+
+	for (size_t window = 0; window < window_count; window++) {
+		const size_t start = window * window_samples;
+		const size_t end = std::min(start + window_samples, sample_count);
+		double square_sum = 0.0;
+		size_t total = 0;
+
+		for (int channel = 0; channel < channel_count; channel++) {
+			const float *data = samples.data(channel);
+			for (size_t sample = start; sample < end; sample++) {
+				const double value = data[sample];
+				square_sum += value * value;
+				total++;
+			}
+		}
+
+		envelope[static_cast<int>(window)] =
+			total ? std::sqrt(square_sum / static_cast<double>(total)) : 0.0;
+	}
+
+	return envelope;
+}
+
+AudioWaveformSync::OffsetResult AudioWaveformSync::EstimateOffset(
+	const core::SampleBuffer &reference, const core::SampleBuffer &candidate,
+	size_t window_samples, int64_t max_offset_samples)
+{
+	if (!window_samples) {
+		return OffsetResult();
+	}
+
+	const QVector<double> reference_envelope =
+		ExtractRmsEnvelope(reference, window_samples);
+	const QVector<double> candidate_envelope =
+		ExtractRmsEnvelope(candidate, window_samples);
+	const int64_t max_offset_windows =
+		max_offset_samples / static_cast<int64_t>(window_samples);
+
+	return EstimateEnvelopeOffset(reference_envelope, candidate_envelope,
+								  window_samples, max_offset_windows);
+}
+
+AudioWaveformSync::OffsetResult AudioWaveformSync::EstimateEnvelopeOffset(
+	const QVector<double> &reference, const QVector<double> &candidate,
+	size_t window_samples, int64_t max_offset_windows)
+{
+	OffsetResult result;
+	if (reference.isEmpty() || candidate.isEmpty() || !window_samples) {
+		return result;
+	}
+
+	double best_score = -2.0;
+	int64_t best_lag = 0;
+
+	for (int64_t lag = -max_offset_windows; lag <= max_offset_windows; lag++) {
+		const int reference_start = static_cast<int>(std::max<int64_t>(0, -lag));
+		const int candidate_start = static_cast<int>(std::max<int64_t>(0, lag));
+		const int overlap = std::min(reference.size() - reference_start,
+									 candidate.size() - candidate_start);
+
+		if (overlap < 2) {
+			continue;
+		}
+
+		double reference_mean = 0.0;
+		double candidate_mean = 0.0;
+		for (int i = 0; i < overlap; i++) {
+			reference_mean += reference.at(reference_start + i);
+			candidate_mean += candidate.at(candidate_start + i);
+		}
+		reference_mean /= static_cast<double>(overlap);
+		candidate_mean /= static_cast<double>(overlap);
+
+		double numerator = 0.0;
+		double reference_energy = 0.0;
+		double candidate_energy = 0.0;
+		for (int i = 0; i < overlap; i++) {
+			const double reference_value =
+				reference.at(reference_start + i) - reference_mean;
+			const double candidate_value =
+				candidate.at(candidate_start + i) - candidate_mean;
+			numerator += reference_value * candidate_value;
+			reference_energy += reference_value * reference_value;
+			candidate_energy += candidate_value * candidate_value;
+		}
+
+		if (qFuzzyIsNull(reference_energy) || qFuzzyIsNull(candidate_energy)) {
+			continue;
+		}
+
+		const double score =
+			numerator / std::sqrt(reference_energy * candidate_energy);
+		if (score > best_score) {
+			best_score = score;
+			best_lag = lag;
+		}
+	}
+
+	if (best_score > -2.0) {
+		result.valid = true;
+		result.confidence = std::max(0.0, best_score);
+		result.offset_samples =
+			best_lag * static_cast<int64_t>(window_samples);
+	}
+
+	return result;
+}
+
+}