fix(crispasr): write piper TTS WAV at the model's native sample rate (#10277)

CrispASR's piper backend returns PCM at the voice's native rate (from the GGUF
piper.sample_rate key: 16 kHz for x_low/low, 22.05 kHz for medium/high) and does
not resample, but the Go WAV encoder hardcoded 24000 Hz. Every piper voice was
therefore written with a wrong header and played back at the wrong pitch/speed.

Read piper.sample_rate from the model's GGUF metadata at Load via the vendored
gguf-parser-go and use it for the WAV header, falling back to the 24 kHz default
for the other CrispASR TTS engines (vibevoice/orpheus/chatterbox/qwen3-tts) that
emit 24 kHz and carry no such key.

Adds unit specs (minimal crafted GGUFs + WAV-header decode) and an env-gated
end-to-end spec (CRISPASR_PIPER_MODEL_PATH). Verified e2e: en_GB-cori-medium
synthesizes a 22050 Hz WAV through backend:piper.


Assisted-by: Claude:claude-opus-4-8 [Claude Code]

Signed-off-by: Ettore Di Giacinto <mudler@localai.io>
Co-authored-by: Ettore Di Giacinto <mudler@localai.io>

Author: localai-bot

backend/go/crispasr/gocrispasr.go

@@ -11,6 +11,7 @@ import (
 
 	"github.com/go-audio/audio"
 	"github.com/go-audio/wav"
+	gguf "github.com/gpustack/gguf-parser-go"
 	"github.com/mudler/LocalAI/pkg/grpc/base"
 	pb "github.com/mudler/LocalAI/pkg/grpc/proto"
 	"github.com/mudler/LocalAI/pkg/utils"
@@ -37,6 +38,39 @@ var (
 
 type CrispASR struct {
 	base.SingleThread
+	// sampleRate is the output rate (Hz) of the loaded TTS engine's PCM, used to
+	// write a correct WAV header. Most CrispASR TTS backends emit 24 kHz, but
+	// piper returns its model's native rate (16 kHz for x_low/low voices,
+	// 22.05 kHz for medium/high), so it is read from the GGUF metadata at Load.
+	sampleRate int
+}
+
+// defaultTTSSampleRate is the output rate assumed for CrispASR TTS engines that
+// don't advertise one in GGUF metadata (vibevoice/orpheus/chatterbox/qwen3-tts
+// all emit 24 kHz). piper is the exception and carries piper.sample_rate.
+const defaultTTSSampleRate = 24000
+
+// piperSampleRate reads the piper.sample_rate metadata key from a GGUF model.
+// CrispASR's piper backend returns PCM at the model's native rate without
+// resampling, so the WAV header must match it. Returns ok=false for non-piper
+// models (key absent) or an unreadable file, letting the caller fall back to
+// defaultTTSSampleRate.
+func piperSampleRate(modelPath string) (int, bool) {
+	// Only scalar architecture keys are read, so skip the large array metadata
+	// (phoneme map) and mmap the header - same rationale as pkg/vram's reader.
+	f, err := gguf.ParseGGUFFile(modelPath, gguf.UseMMap(), gguf.SkipLargeMetadata())
+	if err != nil {
+		return 0, false
+	}
+	kv, ok := f.Header.MetadataKV.Get("piper.sample_rate")
+	if !ok || kv.ValueType != gguf.GGUFMetadataValueTypeUint32 {
+		return 0, false
+	}
+	rate := int(kv.ValueUint32())
+	if rate <= 0 {
+		return 0, false
+	}
+	return rate, true
 }
 
 // splitOption splits a "prefix:value" model option into its key and value,
@@ -103,6 +137,14 @@ func (w *CrispASR) Load(opts *pb.ModelOptions) error {
 		return fmt.Errorf("Failed to load CrispASR transcription model")
 	}
 
+	// Determine the TTS output sample rate for the WAV header. piper voices
+	// carry their native rate in GGUF metadata and CrispASR does not resample;
+	// every other engine emits the 24 kHz default.
+	w.sampleRate = defaultTTSSampleRate
+	if rate, ok := piperSampleRate(opts.ModelFile); ok {
+		w.sampleRate = rate
+	}
+
 	// Load the companion file (codec/tokenizer/s3gen) after the session is open.
 	// rc==0 means success or "not applicable" for the active backend; only a
 	// negative code is fatal.
@@ -390,7 +432,7 @@ func (w *CrispASR) synthesize(text string) ([]float32, error) {
 	}
 	defer CppTTSFree(ptr)
 	src := unsafe.Slice((*float32)(unsafe.Pointer(ptr)), int(n)) //nolint:govet // ptr addresses C-allocated PCM returned across the purego boundary; copied out immediately below, before tts_free.
-	out := make([]float32, int(n)) // copy out of C memory before free
+	out := make([]float32, int(n))                               // copy out of C memory before free
 	copy(out, src)
 	return out, nil
 }
@@ -417,7 +459,7 @@ func (w *CrispASR) TTS(req *pb.TTSRequest) error {
 	if err != nil {
 		return err
 	}
-	return writeWAV24k(req.Dst, pcm)
+	return writeWAV(req.Dst, pcm, w.sampleRate)
 }
 
 // TTSStream is the streaming counterpart to TTS. CrispASR has no progressive
@@ -447,7 +489,7 @@ func (w *CrispASR) TTSStream(req *pb.TTSRequest, results chan []byte) error {
 	}
 	defer func() { _ = os.Remove(dst) }()
 
-	if err := writeWAV24k(dst, pcm); err != nil {
+	if err := writeWAV(dst, pcm, w.sampleRate); err != nil {
 		return err
 	}
 
@@ -459,14 +501,14 @@ func (w *CrispASR) TTSStream(req *pb.TTSRequest, results chan []byte) error {
 	return nil
 }
 
-// writeWAV24k writes pcm as a 24000 Hz, mono, 16-bit PCM WAV at dst.
-func writeWAV24k(dst string, pcm []float32) error {
+// writeWAV writes pcm as a sampleRate Hz, mono, 16-bit PCM WAV at dst.
+func writeWAV(dst string, pcm []float32, sampleRate int) error {
 	f, err := os.Create(dst)
 	if err != nil {
 		return fmt.Errorf("crispasr: create %q: %w", dst, err)
 	}
 
-	enc := wav.NewEncoder(f, 24000, 16, 1, 1)
+	enc := wav.NewEncoder(f, sampleRate, 16, 1, 1)
 	ints := make([]int, len(pcm))
 	for i, s := range pcm {
 		if s > 1 {
@@ -477,7 +519,7 @@ func writeWAV24k(dst string, pcm []float32) error {
 		ints[i] = int(s * 32767)
 	}
 	buf := &audio.IntBuffer{
-		Format:         &audio.Format{NumChannels: 1, SampleRate: 24000},
+		Format:         &audio.Format{NumChannels: 1, SampleRate: sampleRate},
 		Data:           ints,
 		SourceBitDepth: 16,
 	}

backend/go/crispasr/gocrispasr_samplerate_test.go

@@ -0,0 +1,164 @@
+package main
+
+import (
+	"bytes"
+	"encoding/binary"
+	"os"
+	"path/filepath"
+
+	"github.com/go-audio/wav"
+	pb "github.com/mudler/LocalAI/pkg/grpc/proto"
+	. "github.com/onsi/ginkgo/v2"
+	. "github.com/onsi/gomega"
+)
+
+// GGUF metadata value type tags (subset) from the GGUF spec.
+const (
+	ggufTypeUint32 uint32 = 4
+	ggufTypeString uint32 = 8
+)
+
+type ggufKV struct {
+	key   string
+	vtype uint32
+	val   any
+}
+
+// writeMinimalGGUF emits a valid, tensor-less GGUF file carrying only the given
+// metadata key-values. Enough for the header-only parse path piperSampleRate
+// uses; avoids pulling a real multi-MB voice into the test.
+func writeMinimalGGUF(path string, kvs []ggufKV) error {
+	var b bytes.Buffer
+	b.WriteString("GGUF")                                // magic
+	_ = binary.Write(&b, binary.LittleEndian, uint32(3)) // version
+	_ = binary.Write(&b, binary.LittleEndian, uint64(0)) // tensor count
+	_ = binary.Write(&b, binary.LittleEndian, uint64(len(kvs)))
+	for _, kv := range kvs {
+		_ = binary.Write(&b, binary.LittleEndian, uint64(len(kv.key)))
+		b.WriteString(kv.key)
+		_ = binary.Write(&b, binary.LittleEndian, kv.vtype)
+		switch v := kv.val.(type) {
+		case uint32:
+			_ = binary.Write(&b, binary.LittleEndian, v)
+		case string:
+			_ = binary.Write(&b, binary.LittleEndian, uint64(len(v)))
+			b.WriteString(v)
+		}
+	}
+	return os.WriteFile(path, b.Bytes(), 0o644)
+}
+
+// wavSampleRate decodes the WAV header at path and returns its sample rate.
+func wavSampleRate(path string) (int, error) {
+	f, err := os.Open(path)
+	if err != nil {
+		return 0, err
+	}
+	defer func() { _ = f.Close() }()
+	dec := wav.NewDecoder(f)
+	dec.ReadInfo()
+	return int(dec.SampleRate), nil
+}
+
+var _ = Describe("piper sample rate", func() {
+	Context("piperSampleRate", func() {
+		It("reads piper.sample_rate from a piper GGUF (medium = 22050)", func() {
+			p := filepath.Join(GinkgoT().TempDir(), "voice.gguf")
+			Expect(writeMinimalGGUF(p, []ggufKV{
+				{key: "general.architecture", vtype: ggufTypeString, val: "piper"},
+				{key: "piper.sample_rate", vtype: ggufTypeUint32, val: uint32(22050)},
+			})).To(Succeed())
+
+			rate, ok := piperSampleRate(p)
+			Expect(ok).To(BeTrue(), "piper.sample_rate should be found")
+			Expect(rate).To(Equal(22050))
+		})
+
+		It("reads the low-quality rate (16000)", func() {
+			p := filepath.Join(GinkgoT().TempDir(), "voice.gguf")
+			Expect(writeMinimalGGUF(p, []ggufKV{
+				{key: "piper.sample_rate", vtype: ggufTypeUint32, val: uint32(16000)},
+			})).To(Succeed())
+
+			rate, ok := piperSampleRate(p)
+			Expect(ok).To(BeTrue())
+			Expect(rate).To(Equal(16000))
+		})
+
+		It("returns ok=false for a non-piper GGUF (no piper.sample_rate key)", func() {
+			p := filepath.Join(GinkgoT().TempDir(), "other.gguf")
+			Expect(writeMinimalGGUF(p, []ggufKV{
+				{key: "general.architecture", vtype: ggufTypeString, val: "vibevoice"},
+			})).To(Succeed())
+
+			_, ok := piperSampleRate(p)
+			Expect(ok).To(BeFalse())
+		})
+
+		It("returns ok=false for an unreadable/non-GGUF file", func() {
+			p := filepath.Join(GinkgoT().TempDir(), "garbage.gguf")
+			Expect(os.WriteFile(p, []byte("not a gguf"), 0o644)).To(Succeed())
+
+			_, ok := piperSampleRate(p)
+			Expect(ok).To(BeFalse())
+		})
+	})
+
+	// End-to-end through the built .so. Gated on CRISPASR_PIPER_MODEL_PATH (a
+	// real piper voice GGUF) like the other model-backed specs; never runs in
+	// default CI. Proves CrispASR's piper backend output rate flows into the
+	// WAV header instead of the hardcoded 24 kHz default.
+	Context("piper TTS end-to-end", func() {
+		It("writes the WAV at the model's native piper.sample_rate", func() {
+			model := os.Getenv("CRISPASR_PIPER_MODEL_PATH")
+			if model == "" {
+				Skip("set CRISPASR_PIPER_MODEL_PATH to run the piper e2e spec")
+			}
+			ensureLibLoaded()
+
+			expected, ok := piperSampleRate(model)
+			Expect(ok).To(BeTrue(), "model should carry piper.sample_rate metadata")
+
+			w := &CrispASR{}
+			Expect(w.Load(&pb.ModelOptions{
+				ModelFile: model,
+				Options:   []string{"backend:piper"},
+				Threads:   4,
+			})).To(Succeed())
+
+			dst := filepath.Join(GinkgoT().TempDir(), "piper.wav")
+			Expect(w.TTS(&pb.TTSRequest{Text: "Hello from CrispASR piper.", Dst: dst})).To(Succeed())
+
+			info, err := os.Stat(dst)
+			Expect(err).ToNot(HaveOccurred())
+			Expect(info.Size()).To(BeNumerically(">", 1024), "expected a non-trivial WAV")
+
+			rate, err := wavSampleRate(dst)
+			Expect(err).ToNot(HaveOccurred())
+			Expect(rate).To(Equal(expected),
+				"WAV header rate must equal the model's native piper.sample_rate, not the 24k default")
+		})
+	})
+
+	Context("writeWAV", func() {
+		It("writes the WAV header at the given sample rate (22050 for piper, not the 24k default)", func() {
+			dst := filepath.Join(GinkgoT().TempDir(), "out.wav")
+			pcm := make([]float32, 220) // 10 ms of silence is enough for a header
+			Expect(writeWAV(dst, pcm, 22050)).To(Succeed())
+
+			rate, err := wavSampleRate(dst)
+			Expect(err).ToNot(HaveOccurred())
+			Expect(rate).To(Equal(22050))
+		})
+
+		It("writes a 16000 Hz header for low-quality piper voices", func() {
+			dst := filepath.Join(GinkgoT().TempDir(), "out.wav")
+			pcm := make([]float32, 160)
+			Expect(writeWAV(dst, pcm, 16000)).To(Succeed())
+
+			rate, err := wavSampleRate(dst)
+			Expect(err).ToNot(HaveOccurred())
+			Expect(rate).To(Equal(16000))
+		})
+	})
+})