sfx-maker: sfxc - sfxr-style .sfx text presets -> 16-bit WAV synthesis

- waves: square (duty), saw, sine, triangle, pitched noise (seeded, deterministic) - envelope attack/sustain/decay, freq slide, vibrato, arpeggio jump, one-pole low/high-pass filters, clamped output - presets blip/coin/explosion/hurt/jump/laser/powerup with seeded variants; preset writes editable .sfx or renders .wav directly - go tests: parse/validate, determinism, per-preset RMS, WAV header roundtrip Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01MmdG9GqfSWCzts7AkDwRDh
2026-07-14 07:08:04 +02:00
parent ec814c373a
commit e7ac31b5c8
22 changed files with 1028 additions and 0 deletions
--- a/sfx-maker/sfx/params.go
+++ b/sfx-maker/sfx/params.go
@@ -0,0 +1,223 @@
+// Package sfx synthesizes retro game sound effects (sfxr-style) from
+// text parameter files and renders them to 16-bit mono WAV.
+package sfx
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"os"
+	"path/filepath"
+	"strconv"
+	"strings"
+)
+
+// Params describes one sound effect. Zero values mean "off" for the
+// optional effects; Defaults() fills the required fields.
+type Params struct {
+	Name string
+	Wave string // square | saw | sine | triangle | noise
+
+	Volume float64 // 0..1 master gain
+
+	// envelope, seconds
+	Attack  float64 // 0 -> Volume
+	Sustain float64 // hold at Volume
+	Decay   float64 // Volume -> 0
+
+	Freq      float64 // start frequency, Hz
+	FreqSlide float64 // Hz per second, may be negative
+	FreqMin   float64 // clamp; sound stops below this (default 20 Hz)
+
+	Duty float64 // square wave duty cycle 0.05..0.95 (default 0.5)
+
+	VibratoDepth float64 // Hz
+	VibratoRate  float64 // Hz
+
+	ArpFactor float64 // frequency multiplier applied at ArpTime (0 = off)
+	ArpTime   float64 // seconds
+
+	LowPass  float64 // cutoff Hz (0 = off)
+	HighPass float64 // cutoff Hz (0 = off)
+
+	SampleRate int   // default 44100
+	Seed       int64 // noise seed (default 1)
+}
+
+// Defaults returns a Params with sensible base values.
+func Defaults() Params {
+	return Params{
+		Wave:       "square",
+		Volume:     0.7,
+		Attack:     0.01,
+		Sustain:    0.1,
+		Decay:      0.15,
+		Freq:       440,
+		FreqMin:    20,
+		Duty:       0.5,
+		SampleRate: 44100,
+		Seed:       1,
+	}
+}
+
+// Duration is the total length of the sound in seconds.
+func (p *Params) Duration() float64 { return p.Attack + p.Sustain + p.Decay }
+
+// Validate checks ranges and returns a helpful error.
+func (p *Params) Validate() error {
+	switch p.Wave {
+	case "square", "saw", "sine", "triangle", "noise":
+	default:
+		return fmt.Errorf("wave %q must be square, saw, sine, triangle or noise", p.Wave)
+	}
+	if p.Volume < 0 || p.Volume > 1 {
+		return fmt.Errorf("volume %g out of range 0-1", p.Volume)
+	}
+	if p.Attack < 0 || p.Sustain < 0 || p.Decay < 0 {
+		return fmt.Errorf("attack/sustain/decay must be >= 0")
+	}
+	if p.Duration() <= 0 {
+		return fmt.Errorf("total duration is 0 — set attack, sustain and/or decay")
+	}
+	if p.Duration() > 10 {
+		return fmt.Errorf("total duration %.2fs is too long (max 10s)", p.Duration())
+	}
+	if p.Wave != "noise" && (p.Freq <= 0 || p.Freq > 20000) {
+		return fmt.Errorf("freq %g out of range 1-20000 Hz", p.Freq)
+	}
+	if p.Duty < 0.05 || p.Duty > 0.95 {
+		return fmt.Errorf("duty %g out of range 0.05-0.95", p.Duty)
+	}
+	if p.SampleRate < 8000 || p.SampleRate > 96000 {
+		return fmt.Errorf("sample-rate %d out of range 8000-96000", p.SampleRate)
+	}
+	return nil
+}
+
+// ParseFile reads a .sfx file; the name defaults to the file name.
+func ParseFile(path string) (*Params, error) {
+	f, err := os.Open(path)
+	if err != nil {
+		return nil, err
+	}
+	defer f.Close()
+	p, err := Parse(f)
+	if err != nil {
+		return nil, fmt.Errorf("%s: %w", path, err)
+	}
+	if p.Name == "" {
+		p.Name = strings.TrimSuffix(filepath.Base(path), filepath.Ext(path))
+	}
+	return p, nil
+}
+
+// Parse reads the .sfx text format: one "key: value" per line,
+// '#' comments. Unknown keys are errors so typos surface immediately.
+func Parse(r io.Reader) (*Params, error) {
+	p := Defaults()
+	sc := bufio.NewScanner(r)
+	lineNo := 0
+	for sc.Scan() {
+		lineNo++
+		line := strings.TrimSpace(sc.Text())
+		if line == "" || strings.HasPrefix(line, "#") {
+			continue
+		}
+		i := strings.Index(line, ":")
+		if i < 0 {
+			return nil, fmt.Errorf("line %d: want 'key: value', got %q", lineNo, line)
+		}
+		key := strings.ToLower(strings.TrimSpace(line[:i]))
+		val := strings.TrimSpace(line[i+1:])
+		if j := strings.Index(val, " #"); j >= 0 { // trailing comment
+			val = strings.TrimSpace(val[:j])
+		}
+		var err error
+		switch key {
+		case "sfx", "name":
+			p.Name = val
+		case "wave":
+			p.Wave = strings.ToLower(val)
+		case "volume":
+			p.Volume, err = strconv.ParseFloat(val, 64)
+		case "attack":
+			p.Attack, err = strconv.ParseFloat(val, 64)
+		case "sustain":
+			p.Sustain, err = strconv.ParseFloat(val, 64)
+		case "decay":
+			p.Decay, err = strconv.ParseFloat(val, 64)
+		case "freq":
+			p.Freq, err = strconv.ParseFloat(val, 64)
+		case "freq-slide":
+			p.FreqSlide, err = strconv.ParseFloat(val, 64)
+		case "freq-min":
+			p.FreqMin, err = strconv.ParseFloat(val, 64)
+		case "duty":
+			p.Duty, err = strconv.ParseFloat(val, 64)
+		case "vibrato-depth":
+			p.VibratoDepth, err = strconv.ParseFloat(val, 64)
+		case "vibrato-rate":
+			p.VibratoRate, err = strconv.ParseFloat(val, 64)
+		case "arpeggio":
+			p.ArpFactor, err = strconv.ParseFloat(val, 64)
+		case "arpeggio-time":
+			p.ArpTime, err = strconv.ParseFloat(val, 64)
+		case "lowpass":
+			p.LowPass, err = strconv.ParseFloat(val, 64)
+		case "highpass":
+			p.HighPass, err = strconv.ParseFloat(val, 64)
+		case "sample-rate":
+			p.SampleRate, err = strconv.Atoi(val)
+		case "seed":
+			p.Seed, err = strconv.ParseInt(val, 10, 64)
+		default:
+			return nil, fmt.Errorf("line %d: unknown key %q", lineNo, key)
+		}
+		if err != nil {
+			return nil, fmt.Errorf("line %d: %s: bad value %q", lineNo, key, val)
+		}
+	}
+	if err := sc.Err(); err != nil {
+		return nil, err
+	}
+	if err := p.Validate(); err != nil {
+		return nil, err
+	}
+	return &p, nil
+}
+
+// Write renders the params back to the .sfx text format (used by the
+// preset generator so agents get an editable file).
+func (p *Params) Write(w io.Writer, comment string) error {
+	bw := bufio.NewWriter(w)
+	if comment != "" {
+		fmt.Fprintf(bw, "# %s\n", comment)
+	}
+	fmt.Fprintf(bw, "sfx: %s\nwave: %s\nvolume: %g\n", p.Name, p.Wave, p.Volume)
+	fmt.Fprintf(bw, "attack: %g\nsustain: %g\ndecay: %g\n", p.Attack, p.Sustain, p.Decay)
+	if p.Wave != "noise" {
+		fmt.Fprintf(bw, "freq: %g\n", p.Freq)
+	}
+	if p.FreqSlide != 0 {
+		fmt.Fprintf(bw, "freq-slide: %g\n", p.FreqSlide)
+	}
+	if p.Wave == "square" && p.Duty != 0.5 {
+		fmt.Fprintf(bw, "duty: %g\n", p.Duty)
+	}
+	if p.VibratoDepth > 0 && p.VibratoRate > 0 {
+		fmt.Fprintf(bw, "vibrato-depth: %g\nvibrato-rate: %g\n", p.VibratoDepth, p.VibratoRate)
+	}
+	if p.ArpFactor != 0 {
+		fmt.Fprintf(bw, "arpeggio: %g\narpeggio-time: %g\n", p.ArpFactor, p.ArpTime)
+	}
+	if p.LowPass > 0 {
+		fmt.Fprintf(bw, "lowpass: %g\n", p.LowPass)
+	}
+	if p.HighPass > 0 {
+		fmt.Fprintf(bw, "highpass: %g\n", p.HighPass)
+	}
+	if p.Seed != 1 {
+		fmt.Fprintf(bw, "seed: %d\n", p.Seed)
+	}
+	return bw.Flush()
+}
--- a/sfx-maker/sfx/presets.go
+++ b/sfx-maker/sfx/presets.go
@@ -0,0 +1,114 @@
+package sfx
+
+import (
+	"fmt"
+	"math/rand"
+	"sort"
+)
+
+// Preset returns ready-made parameters for classic game sounds.
+// seed 0 gives the canonical version; other seeds vary it slightly so
+// agents can generate alternatives ("give me three coin variants").
+func Preset(name string, seed int64) (*Params, error) {
+	p := Defaults()
+	p.Name = name
+	switch name {
+	case "jump":
+		p.Wave = "square"
+		p.Duty = 0.5
+		p.Freq = 330
+		p.FreqSlide = 900
+		p.Attack = 0.01
+		p.Sustain = 0.08
+		p.Decay = 0.18
+	case "coin":
+		p.Wave = "square"
+		p.Duty = 0.5
+		p.Freq = 988
+		p.ArpFactor = 1.335 // up a fourth: B5 -> E6
+		p.ArpTime = 0.06
+		p.Attack = 0.005
+		p.Sustain = 0.08
+		p.Decay = 0.25
+	case "laser":
+		p.Wave = "saw"
+		p.Freq = 1400
+		p.FreqSlide = -6000
+		p.Attack = 0.005
+		p.Sustain = 0.05
+		p.Decay = 0.12
+		p.HighPass = 300
+	case "explosion":
+		p.Wave = "noise"
+		p.Freq = 900
+		p.FreqSlide = -600
+		p.Attack = 0.01
+		p.Sustain = 0.15
+		p.Decay = 0.55
+		p.LowPass = 2200
+	case "hurt":
+		p.Wave = "saw"
+		p.Freq = 300
+		p.FreqSlide = -700
+		p.Attack = 0.005
+		p.Sustain = 0.04
+		p.Decay = 0.14
+	case "powerup":
+		p.Wave = "square"
+		p.Duty = 0.4
+		p.Freq = 220
+		p.FreqSlide = 700
+		p.VibratoDepth = 25
+		p.VibratoRate = 9
+		p.Attack = 0.01
+		p.Sustain = 0.25
+		p.Decay = 0.25
+	case "blip":
+		p.Wave = "square"
+		p.Duty = 0.4
+		p.Freq = 660
+		p.Attack = 0.002
+		p.Sustain = 0.03
+		p.Decay = 0.05
+	default:
+		return nil, fmt.Errorf("unknown preset %q (available: %s)", name, PresetNames())
+	}
+	if seed != 0 {
+		vary(&p, seed)
+	}
+	if err := p.Validate(); err != nil {
+		return nil, fmt.Errorf("preset %s (seed %d): %w", name, seed, err)
+	}
+	return &p, nil
+}
+
+// vary nudges the tonal parameters deterministically from the seed.
+func vary(p *Params, seed int64) {
+	rng := rand.New(rand.NewSource(seed))
+	jitter := func(v, amount float64) float64 {
+		return v * (1 + amount*(rng.Float64()*2-1))
+	}
+	p.Freq = jitter(p.Freq, 0.15)
+	p.FreqSlide = jitter(p.FreqSlide, 0.25)
+	p.Sustain = jitter(p.Sustain, 0.2)
+	p.Decay = jitter(p.Decay, 0.2)
+	if p.ArpFactor != 0 {
+		p.ArpFactor = jitter(p.ArpFactor, 0.05)
+	}
+	p.Seed = seed // noise variation too
+}
+
+var presetNames = []string{"blip", "coin", "explosion", "hurt", "jump", "laser", "powerup"}
+
+// PresetNames lists the available presets, sorted.
+func PresetNames() string {
+	sort.Strings(presetNames)
+	out := ""
+	for i, n := range presetNames {
+		if i > 0 {
+			out += ", "
+		}
+		out += n
+	}
+	return out
+}
--- a/sfx-maker/sfx/sfx_test.go
+++ b/sfx-maker/sfx/sfx_test.go
@@ -0,0 +1,164 @@
+package sfx
+
+import (
+	"bytes"
+	"math"
+	"strings"
+	"testing"
+)
+
+func TestParseAndValidate(t *testing.T) {
+	src := `
+# a jump
+sfx: jump
+wave: square
+freq: 330
+freq-slide: 900
+attack: 0.01
+sustain: 0.08
+decay: 0.18
+duty: 0.4
+`
+	p, err := Parse(strings.NewReader(src))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if p.Name != "jump" || p.Wave != "square" || p.Freq != 330 || p.Duty != 0.4 {
+		t.Errorf("parsed wrong: %+v", p)
+	}
+	if math.Abs(p.Duration()-0.27) > 1e-9 {
+		t.Errorf("duration = %g, want 0.27", p.Duration())
+	}
+}
+
+func TestParseErrors(t *testing.T) {
+	cases := map[string]string{
+		"unknown key":  "wat: 3\n",
+		"bad wave":     "wave: wobble\n",
+		"bad value":    "freq: abc\n",
+		"zero length":  "attack: 0\nsustain: 0\ndecay: 0\n",
+		"volume range": "volume: 2\n",
+		"duty range":   "duty: 0.99\n",
+	}
+	for name, src := range cases {
+		if _, err := Parse(strings.NewReader(src)); err == nil {
+			t.Errorf("%s: expected error", name)
+		}
+	}
+}
+
+func TestRenderBasics(t *testing.T) {
+	p := Defaults()
+	p.Wave = "sine"
+	p.Attack, p.Sustain, p.Decay = 0.01, 0.05, 0.05
+	samples := Render(&p)
+	want := int(0.11 * 44100)
+	if len(samples) != want {
+		t.Errorf("samples = %d, want %d", len(samples), want)
+	}
+	var peak float64
+	for _, s := range samples {
+		if math.Abs(s) > peak {
+			peak = math.Abs(s)
+		}
+		if s > 1 || s < -1 {
+			t.Fatalf("sample %g out of range", s)
+		}
+	}
+	if peak < 0.5 {
+		t.Errorf("peak %g suspiciously quiet", peak)
+	}
+	// end of decay should be silent-ish
+	tail := samples[len(samples)-10:]
+	for _, s := range tail {
+		if math.Abs(s) > 0.1 {
+			t.Errorf("tail sample %g not decayed", s)
+		}
+	}
+}
+
+func TestRenderDeterministic(t *testing.T) {
+	p := Defaults()
+	p.Wave = "noise"
+	p.Seed = 42
+	a := Render(&p)
+	b := Render(&p)
+	for i := range a {
+		if a[i] != b[i] {
+			t.Fatalf("noise render not deterministic at sample %d", i)
+		}
+	}
+}
+
+func TestAllWavesAndPresets(t *testing.T) {
+	for _, w := range []string{"square", "saw", "sine", "triangle", "noise"} {
+		p := Defaults()
+		p.Wave = w
+		if s := Render(&p); len(s) == 0 {
+			t.Errorf("wave %s rendered nothing", w)
+		}
+	}
+	for _, name := range []string{"blip", "coin", "explosion", "hurt", "jump", "laser", "powerup"} {
+		p, err := Preset(name, 0)
+		if err != nil {
+			t.Errorf("preset %s: %v", name, err)
+			continue
+		}
+		s := Render(p)
+		var sum float64
+		for _, v := range s {
+			sum += v * v
+		}
+		rms := math.Sqrt(sum / float64(len(s)))
+		if rms < 0.01 {
+			t.Errorf("preset %s is nearly silent (rms %g)", name, rms)
+		}
+		// variants stay valid
+		if _, err := Preset(name, 7); err != nil {
+			t.Errorf("preset %s seed 7: %v", name, err)
+		}
+	}
+	if _, err := Preset("nope", 0); err == nil {
+		t.Error("unknown preset should error")
+	}
+}
+
+func TestWAVRoundTrip(t *testing.T) {
+	p := Defaults()
+	samples := Render(&p)
+	var buf bytes.Buffer
+	if err := WriteWAV(&buf, samples, p.SampleRate); err != nil {
+		t.Fatal(err)
+	}
+	sr, bits, ch, dataBytes, err := ReadWAVHeader(&buf)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if sr != 44100 || bits != 16 || ch != 1 {
+		t.Errorf("header: sr=%d bits=%d ch=%d", sr, bits, ch)
+	}
+	if dataBytes != len(samples)*2 {
+		t.Errorf("dataBytes = %d, want %d", dataBytes, len(samples)*2)
+	}
+	if buf.Len() != dataBytes {
+		t.Errorf("body length %d != declared %d", buf.Len(), dataBytes)
+	}
+}
+
+func TestParamsWriteRoundTrip(t *testing.T) {
+	p, err := Preset("coin", 3)
+	if err != nil {
+		t.Fatal(err)
+	}
+	var buf bytes.Buffer
+	if err := p.Write(&buf, "test"); err != nil {
+		t.Fatal(err)
+	}
+	back, err := Parse(&buf)
+	if err != nil {
+		t.Fatalf("re-parse of written .sfx failed: %v\n%s", err, buf.String())
+	}
+	if back.Freq != p.Freq || back.ArpFactor != p.ArpFactor || back.Seed != p.Seed {
+		t.Errorf("roundtrip mismatch: %+v vs %+v", back, p)
+	}
+}
--- a/sfx-maker/sfx/synth.go
+++ b/sfx-maker/sfx/synth.go
@@ -0,0 +1,122 @@
+package sfx
+
+import (
+	"math"
+	"math/rand"
+)
+
+// Render synthesizes the effect into float64 samples in [-1, 1].
+func Render(p *Params) []float64 {
+	sr := float64(p.SampleRate)
+	n := int(p.Duration() * sr)
+	out := make([]float64, n)
+	rng := rand.New(rand.NewSource(p.Seed))
+
+	phase := 0.0
+	noiseVal := 0.0
+	noiseCounter := 0.0
+
+	// one-pole filter states
+	lpState := 0.0
+	hpState := 0.0
+	hpPrevIn := 0.0
+	dt := 1 / sr
+	lpAlpha := 0.0
+	if p.LowPass > 0 {
+		rc := 1 / (2 * math.Pi * p.LowPass)
+		lpAlpha = dt / (rc + dt)
+	}
+	hpAlpha := 0.0
+	if p.HighPass > 0 {
+		rc := 1 / (2 * math.Pi * p.HighPass)
+		hpAlpha = rc / (rc + dt)
+	}
+
+	for i := 0; i < n; i++ {
+		t := float64(i) / sr
+
+		f := p.Freq + p.FreqSlide*t
+		if p.ArpFactor != 0 && p.ArpTime > 0 && t >= p.ArpTime {
+			f *= p.ArpFactor
+		}
+		if p.VibratoDepth > 0 && p.VibratoRate > 0 {
+			f += p.VibratoDepth * math.Sin(2*math.Pi*p.VibratoRate*t)
+		}
+		if f < p.FreqMin {
+			f = p.FreqMin
+		}
+
+		var s float64
+		if p.Wave == "noise" {
+			// pitched noise: new random value f*4 times per second
+			noiseCounter += f * 4 * dt
+			if noiseCounter >= 1 || i == 0 {
+				noiseCounter = math.Mod(noiseCounter, 1)
+				noiseVal = rng.Float64()*2 - 1
+			}
+			s = noiseVal
+		} else {
+			phase += f * dt
+			ph := math.Mod(phase, 1)
+			switch p.Wave {
+			case "square":
+				if ph < p.Duty {
+					s = 1
+				} else {
+					s = -1
+				}
+			case "saw":
+				s = 2*ph - 1
+			case "triangle":
+				if ph < 0.5 {
+					s = 4*ph - 1
+				} else {
+					s = 3 - 4*ph
+				}
+			case "sine":
+				s = math.Sin(2 * math.Pi * ph)
+			}
+		}
+
+		s *= envelope(p, t)
+
+		if lpAlpha > 0 {
+			lpState += lpAlpha * (s - lpState)
+			s = lpState
+		}
+		if hpAlpha > 0 {
+			hpState = hpAlpha * (hpState + s - hpPrevIn)
+			hpPrevIn = s
+			s = hpState
+		}
+
+		s *= p.Volume
+		if s > 1 {
+			s = 1
+		} else if s < -1 {
+			s = -1
+		}
+		out[i] = s
+	}
+	return out
+}
+
+// envelope is a linear attack / sustain / decay gain in 0..1.
+func envelope(p *Params, t float64) float64 {
+	switch {
+	case t < p.Attack:
+		return t / p.Attack
+	case t < p.Attack+p.Sustain:
+		return 1
+	default:
+		d := t - p.Attack - p.Sustain
+		if p.Decay <= 0 {
+			return 0
+		}
+		g := 1 - d/p.Decay
+		if g < 0 {
+			g = 0
+		}
+		return g
+	}
+}
--- a/sfx-maker/sfx/wav.go
+++ b/sfx-maker/sfx/wav.go
@@ -0,0 +1,54 @@
+package sfx
+
+import (
+	"encoding/binary"
+	"fmt"
+	"io"
+	"math"
+)
+
+// WriteWAV encodes samples ([-1,1] floats) as a 16-bit mono PCM WAV.
+func WriteWAV(w io.Writer, samples []float64, sampleRate int) error {
+	dataLen := len(samples) * 2
+	var hdr [44]byte
+	copy(hdr[0:4], "RIFF")
+	binary.LittleEndian.PutUint32(hdr[4:8], uint32(36+dataLen))
+	copy(hdr[8:12], "WAVE")
+	copy(hdr[12:16], "fmt ")
+	binary.LittleEndian.PutUint32(hdr[16:20], 16)                   // fmt chunk size
+	binary.LittleEndian.PutUint16(hdr[20:22], 1)                    // PCM
+	binary.LittleEndian.PutUint16(hdr[22:24], 1)                    // mono
+	binary.LittleEndian.PutUint32(hdr[24:28], uint32(sampleRate))   // sample rate
+	binary.LittleEndian.PutUint32(hdr[28:32], uint32(sampleRate*2)) // byte rate
+	binary.LittleEndian.PutUint16(hdr[32:34], 2)                    // block align
+	binary.LittleEndian.PutUint16(hdr[34:36], 16)                   // bits per sample
+	copy(hdr[36:40], "data")
+	binary.LittleEndian.PutUint32(hdr[40:44], uint32(dataLen))
+	if _, err := w.Write(hdr[:]); err != nil {
+		return err
+	}
+	buf := make([]byte, 2*len(samples))
+	for i, s := range samples {
+		v := int16(math.Round(s * 32767))
+		binary.LittleEndian.PutUint16(buf[i*2:], uint16(v))
+	}
+	_, err := w.Write(buf)
+	return err
+}
+
+// ReadWAVHeader sanity-parses a WAV header (used in tests and info).
+func ReadWAVHeader(r io.Reader) (sampleRate, bits, channels, dataBytes int, err error) {
+	var hdr [44]byte
+	if _, err = io.ReadFull(r, hdr[:]); err != nil {
+		return
+	}
+	if string(hdr[0:4]) != "RIFF" || string(hdr[8:12]) != "WAVE" {
+		err = fmt.Errorf("not a WAV file")
+		return
+	}
+	channels = int(binary.LittleEndian.Uint16(hdr[22:24]))
+	sampleRate = int(binary.LittleEndian.Uint32(hdr[24:28]))
+	bits = int(binary.LittleEndian.Uint16(hdr[34:36]))
+	dataBytes = int(binary.LittleEndian.Uint32(hdr[40:44]))
+	return
+}