feat: add wav file source for offline pipeline

docs/README.md

@@ -10,6 +10,12 @@
 - `go run ./cmd/fmrtx --simulate-tx --simulate-output build/sim/simulated-soapy.iqf32 --simulate-duration 250ms`
 - `go run ./cmd/offline -duration 500ms -output build/offline/composite.iqf32`
 
+### Audio source modes
+
+Current no-hardware sources:
+- generated stereo tones via config
+- 16-bit PCM WAV file input via `audio.inputPath`
+
 ### Tone configuration
 
 The current no-hardware source can be parameterized via config:

internal/audio/wav.go

@@ -0,0 +1,74 @@
+package audio
+
+import (
+    "encoding/binary"
+    "fmt"
+    "io"
+    "os"
+)
+
+type WAVSource struct {
+    frames []Frame
+    index  int
+}
+
+func LoadWAVSource(path string) (*WAVSource, error) {
+    f, err := os.Open(path)
+    if err != nil {
+        return nil, err
+    }
+    defer f.Close()
+
+    header := make([]byte, 44)
+    if _, err := io.ReadFull(f, header); err != nil {
+        return nil, fmt.Errorf("read wav header: %w", err)
+    }
+    if string(header[0:4]) != "RIFF" || string(header[8:12]) != "WAVE" {
+        return nil, fmt.Errorf("unsupported wav header")
+    }
+
+    channels := binary.LittleEndian.Uint16(header[22:24])
+    bitsPerSample := binary.LittleEndian.Uint16(header[34:36])
+    dataSize := binary.LittleEndian.Uint32(header[40:44])
+
+    if bitsPerSample != 16 {
+        return nil, fmt.Errorf("only 16-bit PCM wav supported")
+    }
+    if channels != 1 && channels != 2 {
+        return nil, fmt.Errorf("only mono/stereo wav supported")
+    }
+
+    raw := make([]byte, dataSize)
+    if _, err := io.ReadFull(f, raw); err != nil {
+        return nil, fmt.Errorf("read wav data: %w", err)
+    }
+
+    step := int(channels) * 2
+    frames := make([]Frame, 0, len(raw)/step)
+    for i := 0; i+step <= len(raw); i += step {
+        l := pcm16ToSample(int16(binary.LittleEndian.Uint16(raw[i : i+2])))
+        r := l
+        if channels == 2 {
+            r = pcm16ToSample(int16(binary.LittleEndian.Uint16(raw[i+2 : i+4])))
+        }
+        frames = append(frames, NewFrame(l, r))
+    }
+
+    return &WAVSource{frames: frames}, nil
+}
+
+func (s *WAVSource) NextFrame() Frame {
+    if len(s.frames) == 0 {
+        return NewFrame(0, 0)
+    }
+    frame := s.frames[s.index]
+    s.index++
+    if s.index >= len(s.frames) {
+        s.index = 0
+    }
+    return frame
+}
+
+func pcm16ToSample(v int16) Sample {
+    return Sample(float64(v) / 32768.0).Clamp()
+}

internal/audio/wav_test.go

@@ -0,0 +1,32 @@
+package audio
+
+import (
+    "os"
+    "path/filepath"
+    "testing"
+)
+
+func TestPCM16ToSample(t *testing.T) {
+    if pcm16ToSample(32767) <= 0 {
+        t.Fatal("expected positive sample")
+    }
+}
+
+func TestLoadWAVSource(t *testing.T) {
+    dir := t.TempDir()
+    path := filepath.Join(dir, "test.wav")
+    wav := []byte{
+        'R','I','F','F', 52,0,0,0, 'W','A','V','E',
+        'f','m','t',' ', 16,0,0,0, 1,0, 1,0, 0x80,0xbb,0x00,0x00, 0x00,0x77,0x01,0x00, 2,0, 16,0,
+        'd','a','t','a', 8,0,0,0,
+        0,0, 255,127, 0,128, 0,0,
+    }
+    if err := os.WriteFile(path, wav, 0o644); err != nil {
+        t.Fatalf("write wav: %v", err)
+    }
+    src, err := LoadWAVSource(path)
+    if err != nil {
+        t.Fatalf("LoadWAVSource failed: %v", err)
+    }
+    _ = src.NextFrame()
+}

internal/offline/generator.go

@@ -16,6 +16,10 @@ import (
     "github.com/jan/fm-rds-tx/internal/stereo"
 )
 
+type frameSource interface {
+    NextFrame() audio.Frame
+}
+
 type Generator struct {
     cfg cfgpkg.Config
 }
@@ -24,6 +28,15 @@ func NewGenerator(cfg cfgpkg.Config) *Generator {
     return &Generator{cfg: cfg}
 }
 
+func (g *Generator) sourceFor(sampleRate float64) frameSource {
+    if g.cfg.Audio.InputPath != "" {
+        if src, err := audio.LoadWAVSource(g.cfg.Audio.InputPath); err == nil {
+            return src
+        }
+    }
+    return audio.NewConfiguredToneSource(sampleRate, g.cfg.Audio.ToneLeftHz, g.cfg.Audio.ToneRightHz, g.cfg.Audio.ToneAmplitude)
+}
+
 func (g *Generator) GenerateFrame(duration time.Duration) *output.CompositeFrame {
     sampleRate := float64(g.cfg.FM.CompositeRateHz)
     if sampleRate <= 0 {
@@ -55,7 +68,7 @@ func (g *Generator) GenerateFrame(duration time.Duration) *output.CompositeFrame
     })
     rdsSamples := rdsEnc.Generate(samples)
 
-    source := audio.NewConfiguredToneSource(sampleRate, g.cfg.Audio.ToneLeftHz, g.cfg.Audio.ToneRightHz, g.cfg.Audio.ToneAmplitude)
+    source := g.sourceFor(sampleRate)
 
     for i := 0; i < samples; i++ {
         t := float64(i) / sampleRate
@@ -108,5 +121,9 @@ func (g *Generator) WriteFile(path string, duration time.Duration) error {
 }
 
 func (g *Generator) Summary(duration time.Duration) string {
-    return fmt.Sprintf("offline frame: freq=%.1fMHz sampleRate=%d duration=%s outputDrive=%.2f stereo=%t rds=%t toneL=%.1f toneR=%.1f", g.cfg.FM.FrequencyMHz, g.cfg.FM.CompositeRateHz, duration.String(), g.cfg.FM.OutputDrive, g.cfg.FM.StereoEnabled, g.cfg.RDS.Enabled, g.cfg.Audio.ToneLeftHz, g.cfg.Audio.ToneRightHz)
+    source := "tones"
+    if g.cfg.Audio.InputPath != "" {
+        source = g.cfg.Audio.InputPath
+    }
+    return fmt.Sprintf("offline frame: freq=%.1fMHz sampleRate=%d duration=%s outputDrive=%.2f stereo=%t rds=%t source=%s", g.cfg.FM.FrequencyMHz, g.cfg.FM.CompositeRateHz, duration.String(), g.cfg.FM.OutputDrive, g.cfg.FM.StereoEnabled, g.cfg.RDS.Enabled, source)
 }