Add FLAC audio quality analysis and spectrum visualization (#110)

Introduces backend support for analyzing FLAC audio files, including technical metrics and frequency spectrum extraction. Adds frontend components and hooks for file selection, analysis, and visualization, integrating a new Audio Quality Analyzer dialog into the UI. Updates types and dependencies to support audio analysis features.

backend/analysis.go

@@ -0,0 +1,181 @@
+package backend
+
+import (
+	"fmt"
+	"math"
+	"os"
+
+	"github.com/go-flac/go-flac"
+	mewflac "github.com/mewkiz/flac"
+)
+
+// AnalysisResult contains the audio analysis data
+type AnalysisResult struct {
+	FilePath      string        `json:"file_path"`
+	SampleRate    uint32        `json:"sample_rate"`
+	Channels      uint8         `json:"channels"`
+	BitsPerSample uint8         `json:"bits_per_sample"`
+	TotalSamples  uint64        `json:"total_samples"`
+	Duration      float64       `json:"duration"`
+	BitDepth      string        `json:"bit_depth"`
+	DynamicRange  float64       `json:"dynamic_range"`
+	PeakAmplitude float64       `json:"peak_amplitude"`
+	RMSLevel      float64       `json:"rms_level"`
+	Spectrum      *SpectrumData `json:"spectrum,omitempty"`
+}
+
+// AnalyzeTrack performs audio analysis on a FLAC file
+func AnalyzeTrack(filepath string) (*AnalysisResult, error) {
+	if !fileExists(filepath) {
+		return nil, fmt.Errorf("file does not exist: %s", filepath)
+	}
+
+	// Parse FLAC file
+	f, err := flac.ParseFile(filepath)
+	if err != nil {
+		return nil, fmt.Errorf("failed to parse FLAC file: %w", err)
+	}
+
+	result := &AnalysisResult{
+		FilePath: filepath,
+	}
+
+	// Extract basic audio properties from STREAMINFO block
+	if len(f.Meta) > 0 {
+		streamInfo := f.Meta[0]
+		if streamInfo.Type == flac.StreamInfo {
+			// Read STREAMINFO data
+			data := streamInfo.Data
+			if len(data) >= 18 {
+				// Sample rate (bits 10-29 of bytes 10-13)
+				result.SampleRate = uint32(data[10])<<12 | uint32(data[11])<<4 | uint32(data[12])>>4
+
+				// Channels (bits 30-32 of byte 12)
+				result.Channels = ((data[12] >> 1) & 0x07) + 1
+
+				// Bits per sample (bits 33-37 of bytes 12-13)
+				result.BitsPerSample = ((data[12]&0x01)<<4 | data[13]>>4) + 1
+
+				// Total samples (bits 38-73 of bytes 13-17)
+				result.TotalSamples = uint64(data[13]&0x0F)<<32 |
+					uint64(data[14])<<24 |
+					uint64(data[15])<<16 |
+					uint64(data[16])<<8 |
+					uint64(data[17])
+
+				// Calculate duration
+				if result.SampleRate > 0 {
+					result.Duration = float64(result.TotalSamples) / float64(result.SampleRate)
+				}
+
+				// Read min/max frame size and block size for additional analysis
+				// Min block size (bytes 0-1)
+				// Max block size (bytes 2-3)
+				// These can give us hints about encoding quality
+			}
+		}
+	}
+
+	// Analyze spectrum and calculate real audio metrics
+	spectrum, err := AnalyzeSpectrum(filepath)
+	if err != nil {
+		// Log error but continue
+		fmt.Printf("Warning: failed to analyze spectrum: %v\n", err)
+	} else {
+		result.Spectrum = spectrum
+		// Calculate dynamic range, peak, and RMS from decoded samples
+		calculateRealAudioMetrics(result, filepath)
+	}
+
+	// Set bit depth
+	result.BitDepth = fmt.Sprintf("%d-bit", result.BitsPerSample)
+
+	return result, nil
+}
+
+// calculateRealAudioMetrics calculates actual dynamic range, peak, and RMS from decoded audio
+func calculateRealAudioMetrics(result *AnalysisResult, filepath string) {
+	// Decode FLAC to get actual samples
+	samples, err := decodeFLACForMetrics(filepath)
+	if err != nil {
+		return
+	}
+
+	// Calculate peak amplitude
+	var peak float64
+	var sumSquares float64
+
+	for _, sample := range samples {
+		absVal := sample
+		if absVal < 0 {
+			absVal = -absVal
+		}
+		if absVal > peak {
+			peak = absVal
+		}
+		sumSquares += sample * sample
+	}
+
+	// Convert peak to dB (reference: 1.0 = 0 dBFS)
+	peakDB := 20.0 * math.Log10(peak)
+	result.PeakAmplitude = peakDB
+
+	// Calculate RMS (Root Mean Square)
+	rms := math.Sqrt(sumSquares / float64(len(samples)))
+	rmsDB := 20.0 * math.Log10(rms)
+	result.RMSLevel = rmsDB
+
+	// Dynamic range is the difference between peak and RMS
+	result.DynamicRange = peakDB - rmsDB
+}
+
+// decodeFLACForMetrics decodes FLAC file and returns normalized samples for metric calculation
+func decodeFLACForMetrics(filepath string) ([]float64, error) {
+	stream, err := mewflac.ParseFile(filepath)
+	if err != nil {
+		return nil, err
+	}
+	defer stream.Close()
+
+	// Limit samples to prevent memory issues (10 million samples = ~3.8 minutes at 44.1kHz)
+	maxSamples := 10000000
+	samples := make([]float64, 0, maxSamples)
+
+	// Read all audio frames
+	for {
+		frame, err := stream.ParseNext()
+		if err != nil {
+			break
+		}
+
+		// Get samples from first channel (mono or left channel)
+		var channelSamples []int32
+		if len(frame.Subframes) > 0 {
+			channelSamples = frame.Subframes[0].Samples
+		}
+
+		// Normalize samples to -1.0 to 1.0 range
+		maxVal := float64(int64(1) << (stream.Info.BitsPerSample - 1))
+		for _, sample := range channelSamples {
+			if len(samples) >= maxSamples {
+				return samples, nil
+			}
+			normalized := float64(sample) / maxVal
+			samples = append(samples, normalized)
+		}
+
+		if len(samples) >= maxSamples {
+			break
+		}
+	}
+
+	return samples, nil
+}
+
+func GetFileSize(filepath string) (int64, error) {
+	info, err := os.Stat(filepath)
+	if err != nil {
+		return 0, err
+	}
+	return info.Size(), nil
+}