refactor: reorganize monolithic main package into focused packages

Move the executable entry point to `src/cmd/captioneer` and split audio, capture, config, caption, and model logic into separate packages under `src/`. Update README with new build/run commands and a package-overview section.

src/captions/processor.go

@@ -0,0 +1,120 @@
+// Package captions turns audio packets into fixed or speech-aware captions.
+package captions
+
+import (
+	"fmt"
+	"io"
+
+	"tea.chunkbyte.com/kato/captioneer/src/audio"
+	"tea.chunkbyte.com/kato/captioneer/src/config"
+	"tea.chunkbyte.com/kato/captioneer/src/models"
+)
+
+type Processor struct {
+	settings  config.Settings
+	resources *models.Resources
+	output    io.Writer
+
+	fixedSamples   []float32
+	previewSamples []float32
+	previewActive  bool
+	previewVisible bool
+	nextPreviewAt  int
+	totalSamples   int
+}
+
+func New(settings config.Settings, resources *models.Resources, output io.Writer) *Processor {
+	return &Processor{
+		settings:      settings,
+		resources:     resources,
+		output:        output,
+		nextPreviewAt: audio.DurationSamples(settings.ChunkDuration),
+	}
+}
+
+func (p *Processor) Accept(samples []float32) {
+	if len(samples) == 0 {
+		return
+	}
+	if p.settings.Mode == config.ModeFixed {
+		p.acceptFixed(samples)
+		return
+	}
+	p.acceptVAD(samples)
+}
+
+func (p *Processor) Flush() {
+	if p.settings.Mode == config.ModeFixed {
+		if len(p.fixedSamples) > 0 {
+			p.emitCommitted(p.totalSamples, p.totalSamples+len(p.fixedSamples), p.fixedSamples)
+		}
+		return
+	}
+	p.resources.FlushVAD()
+	p.drainVAD()
+	p.clearPreview()
+}
+
+func (p *Processor) acceptFixed(samples []float32) {
+	p.fixedSamples = append(p.fixedSamples, samples...)
+	chunkSize := audio.DurationSamples(p.settings.ChunkDuration)
+	for len(p.fixedSamples) >= chunkSize {
+		p.emitCommitted(p.totalSamples, p.totalSamples+chunkSize, p.fixedSamples[:chunkSize])
+		p.fixedSamples = p.fixedSamples[chunkSize:]
+		p.totalSamples += chunkSize
+	}
+}
+
+func (p *Processor) acceptVAD(samples []float32) {
+	p.totalSamples += len(samples)
+	p.resources.AcceptVAD(samples)
+
+	if p.previewActive || audio.RMSDBFS(samples) >= p.settings.PreviewThresholdDB {
+		p.previewActive = true
+		p.previewSamples = append(p.previewSamples, samples...)
+		if len(p.previewSamples) >= p.nextPreviewAt {
+			p.emitPreview(p.previewSamples)
+			p.nextPreviewAt += audio.DurationSamples(p.settings.ChunkDuration)
+		}
+	}
+	p.drainVAD()
+}
+
+func (p *Processor) drainVAD() {
+	for {
+		segment, ok := p.resources.NextSpeechSegment()
+		if !ok {
+			return
+		}
+		p.clearPreview()
+		p.emitCommitted(segment.Start, segment.Start+len(segment.Samples), segment.Samples)
+		p.previewSamples = nil
+		p.previewActive = false
+		p.nextPreviewAt = audio.DurationSamples(p.settings.ChunkDuration)
+	}
+}
+
+func (p *Processor) emitPreview(samples []float32) {
+	text := p.resources.Decode(samples)
+	if text == "" {
+		return
+	}
+	fmt.Fprintf(p.output, "\r\033[2K… %s", text)
+	p.previewVisible = true
+}
+
+func (p *Processor) emitCommitted(start, end int, samples []float32) {
+	text := p.resources.Decode(samples)
+	if text == "" {
+		return
+	}
+	p.clearPreview()
+	fmt.Fprintf(p.output, "[%s-%s] %s\n", audio.FormatTime(start), audio.FormatTime(end), text)
+}
+
+func (p *Processor) clearPreview() {
+	if p.previewVisible {
+		fmt.Fprint(p.output, "\r\033[2K")
+		p.previewVisible = false
+	}
+}