feat: add lossless flac to wav converter

2026-08-05 22:51:43 +02:00
parent eea049aae9
commit b3777bf8eb
5 changed files with 496 additions and 0 deletions
@@ -0,0 +1,189 @@
+package audio
+
+import (
+	"bufio"
+	"context"
+	"encoding/binary"
+	"errors"
+	"fmt"
+	"io"
+	"math"
+	"os"
+	"path/filepath"
+
+	"github.com/mathismqn/godeez/internal/fsutil"
+	"github.com/mewkiz/flac"
+)
+
+const (
+	headerSize       = 44
+	formatPCM        = 1
+	ctxCheckInterval = 64
+	maxDataSize      = math.MaxUint32 - (headerSize - 8)
+)
+
+func FLACToWAV(ctx context.Context, srcPath, dstPath string) error {
+	stream, err := flac.Open(srcPath)
+	if err != nil {
+		return err
+	}
+	defer stream.Close()
+
+	info := stream.Info
+	bytesPerSample, err := bytesPerSample(info.BitsPerSample)
+	if err != nil {
+		return err
+	}
+	if info.NChannels < 1 || info.NChannels > 2 {
+		return fmt.Errorf("unsupported channel count: %d", info.NChannels)
+	}
+	if size := int64(info.NSamples) * int64(info.NChannels) * int64(bytesPerSample); size > maxDataSize {
+		return fmt.Errorf("audio data of %d bytes exceeds the wav format limit", size)
+	}
+
+	file, err := os.CreateTemp(filepath.Dir(dstPath), fsutil.PartPattern)
+	if err != nil {
+		return err
+	}
+	tmpPath := file.Name()
+	done := false
+	defer func() {
+		if !done {
+			file.Close()
+			os.Remove(tmpPath)
+		}
+	}()
+
+	w := bufio.NewWriter(file)
+	if err := writeHeader(w, info.SampleRate, info.NChannels, info.BitsPerSample, 0); err != nil {
+		return err
+	}
+
+	dataSize, err := writeSamples(ctx, w, stream, int(info.NChannels), bytesPerSample)
+	if err != nil {
+		return err
+	}
+	if dataSize > maxDataSize {
+		return fmt.Errorf("audio data of %d bytes exceeds the wav format limit", dataSize)
+	}
+	if dataSize%2 != 0 {
+		if err := w.WriteByte(0); err != nil {
+			return err
+		}
+	}
+	if err := w.Flush(); err != nil {
+		return err
+	}
+	if err := patchSizes(file, dataSize); err != nil {
+		return err
+	}
+
+	if err := file.Sync(); err != nil {
+		return err
+	}
+	if err := file.Close(); err != nil {
+		return err
+	}
+	if err := os.Rename(tmpPath, dstPath); err != nil {
+		return err
+	}
+	done = true
+
+	return nil
+}
+
+func bytesPerSample(bitsPerSample uint8) (int, error) {
+	switch bitsPerSample {
+	case 8, 16, 24:
+		return int(bitsPerSample) / 8, nil
+	default:
+		return 0, fmt.Errorf("unsupported bit depth: %d", bitsPerSample)
+	}
+}
+
+func writeHeader(w io.Writer, sampleRate uint32, nChannels, bitsPerSample uint8, dataSize uint32) error {
+	blockAlign := uint32(nChannels) * uint32(bitsPerSample) / 8
+
+	header := make([]byte, 0, headerSize)
+	header = append(header, "RIFF"...)
+	header = binary.LittleEndian.AppendUint32(header, uint32(headerSize-8)+dataSize)
+	header = append(header, "WAVE"...)
+	header = append(header, "fmt "...)
+	header = binary.LittleEndian.AppendUint32(header, 16)
+	header = binary.LittleEndian.AppendUint16(header, formatPCM)
+	header = binary.LittleEndian.AppendUint16(header, uint16(nChannels))
+	header = binary.LittleEndian.AppendUint32(header, sampleRate)
+	header = binary.LittleEndian.AppendUint32(header, sampleRate*blockAlign)
+	header = binary.LittleEndian.AppendUint16(header, uint16(blockAlign))
+	header = binary.LittleEndian.AppendUint16(header, uint16(bitsPerSample))
+	header = append(header, "data"...)
+	header = binary.LittleEndian.AppendUint32(header, dataSize)
+
+	_, err := w.Write(header)
+
+	return err
+}
+
+func writeSamples(ctx context.Context, w io.Writer, stream *flac.Stream, nChannels, bytesPerSample int) (int64, error) {
+	var dataSize int64
+	buf := make([]byte, 4)
+
+	for i := 0; ; i++ {
+		if i%ctxCheckInterval == 0 {
+			select {
+			case <-ctx.Done():
+				return dataSize, ctx.Err()
+			default:
+			}
+		}
+
+		frame, err := stream.ParseNext()
+		if err != nil {
+			if errors.Is(err, io.EOF) {
+				break
+			}
+			return dataSize, err
+		}
+		if len(frame.Subframes) != nChannels {
+			return dataSize, fmt.Errorf("frame %d has %d channels, want %d", frame.Num, len(frame.Subframes), nChannels)
+		}
+
+		for i := range frame.Subframes[0].Samples {
+			for _, subframe := range frame.Subframes {
+				putSample(buf, subframe.Samples[i], bytesPerSample)
+				if _, err := w.Write(buf[:bytesPerSample]); err != nil {
+					return dataSize, err
+				}
+				dataSize += int64(bytesPerSample)
+			}
+		}
+	}
+
+	return dataSize, nil
+}
+
+func putSample(buf []byte, sample int32, bytesPerSample int) {
+	if bytesPerSample == 1 {
+		buf[0] = byte(sample + 128)
+		return
+	}
+
+	value := uint32(sample)
+	for i := range bytesPerSample {
+		buf[i] = byte(value >> (8 * i))
+	}
+}
+
+func patchSizes(file *os.File, dataSize int64) error {
+	buf := make([]byte, 4)
+
+	binary.LittleEndian.PutUint32(buf, uint32(headerSize-8+dataSize+dataSize%2))
+	if _, err := file.WriteAt(buf, 4); err != nil {
+		return err
+	}
+
+	binary.LittleEndian.PutUint32(buf, uint32(dataSize))
+	_, err := file.WriteAt(buf, headerSize-4)
+
+	return err
+}