Maven/cmd/mavttsd/piper_handler.go

package main

import (
	"bytes"
	"context"
	"encoding/binary"
	"fmt"
	"io"
	"os/exec"

	"github.com/kami/maven/internal/audio"
	"github.com/kami/maven/internal/tts"
	"github.com/kami/maven/internal/worker"
)

type piperHandler struct {
	piperPath     string
	modelPath     string
	configPath    string
	espeakData    string
	tashkeelModel string
	// lexicon rewrites service ids and Latin names into the spelling the
	// Russian voice reads correctly (Vikunja #458). Nil-safe: an unconfigured
	// dictionary rewrites nothing.
	lexicon *tts.Lexicon
}

func newPiperHandler(piperPath, modelPath, espeakData, tashkeelModel string, lexicon *tts.Lexicon) *piperHandler {
	return &piperHandler{
		piperPath:     piperPath,
		modelPath:     modelPath,
		configPath:    modelPath + ".json",
		espeakData:    espeakData,
		tashkeelModel: tashkeelModel,
		lexicon:       lexicon,
	}
}

func (h *piperHandler) Synthesize(ctx context.Context, req worker.SynthesizeReq) (worker.SynthesizeResp, error) {
	var stderr bytes.Buffer

	args := []string{
		"--model", h.modelPath,
		"--config", h.configPath,
		"--output_raw",
		"--quiet",
	}
	if h.espeakData != "" {
		args = append(args, "--espeak_data", h.espeakData)
	}
	if h.tashkeelModel != "" {
		args = append(args, "--tashkeel_model", h.tashkeelModel)
	}

	cmd := exec.CommandContext(ctx, h.piperPath, args...)
	cmd.Stderr = &stderr

	stdin, err := cmd.StdinPipe()
	if err != nil {
		return worker.SynthesizeResp{}, fmt.Errorf("piper: stdin pipe: %w", err)
	}

	stdout, err := cmd.StdoutPipe()
	if err != nil {
		stdin.Close()
		return worker.SynthesizeResp{}, fmt.Errorf("piper: stdout pipe: %w", err)
	}

	if err := cmd.Start(); err != nil {
		stdin.Close()
		stdout.Close()
		return worker.SynthesizeResp{}, fmt.Errorf("piper: start: %w", err)
	}

	// The dictionary is applied here, at the last edge before the voice: every
	// caller's text passes through this one point, and nothing upstream has to
	// know how a name is spelled out loud.
	text := req.Text
	if h.lexicon != nil {
		text = h.lexicon.Apply(text)
	}
	if _, err := io.WriteString(stdin, text); err != nil {
		stdin.Close()
		stdout.Close()
		_ = cmd.Wait()
		return worker.SynthesizeResp{}, fmt.Errorf("piper: write text: %w", err)
	}
	stdin.Close()

	rawPCM, readErr := io.ReadAll(stdout)
	stdout.Close()

	waitErr := cmd.Wait()
	if waitErr != nil {
		errMsg := stderr.String()
		if errMsg != "" {
			return worker.SynthesizeResp{}, fmt.Errorf("piper: %s: %s", waitErr, errMsg)
		}
		return worker.SynthesizeResp{}, fmt.Errorf("piper: %w", waitErr)
	}
	if readErr != nil {
		return worker.SynthesizeResp{}, fmt.Errorf("piper: read stdout: %w", readErr)
	}

	if len(rawPCM) == 0 {
		return worker.SynthesizeResp{}, fmt.Errorf("piper: no audio output")
	}

	resampled := resample22050To16000(rawPCM)

	return worker.SynthesizeResp{
		Audio: audio.Audio{
			Format: audio.PCM16kMono,
			Bytes:  resampled,
		},
	}, nil
}

// resample22050To16000 converts raw 16-bit PCM from 22050 Hz to 16000 Hz
// using linear interpolation.
func resample22050To16000(input []byte) []byte {
	if len(input) < 2 {
		return nil
	}

	nSamples := len(input) / 2
	outSamples := int(float64(nSamples) * 16000.0 / 22050.0)
	output := make([]byte, outSamples*2)

	ratio := 22050.0 / 16000.0

	for i := 0; i < outSamples; i++ {
		srcPos := float64(i) * ratio
		srcIdx := int(srcPos)
		frac := srcPos - float64(srcIdx)

		if srcIdx >= nSamples-1 {
			v := int16(binary.LittleEndian.Uint16(input[(nSamples-1)*2:]))
			binary.LittleEndian.PutUint16(output[i*2:], uint16(v))
			continue
		}

		v0 := int16(binary.LittleEndian.Uint16(input[srcIdx*2:]))
		v1 := int16(binary.LittleEndian.Uint16(input[(srcIdx+1)*2:]))

		interpolated := int16(float64(v0)*(1-frac) + float64(v1)*frac)
		binary.LittleEndian.PutUint16(output[i*2:], uint16(interpolated))
	}

	return output
}