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third_party/sendspin-go/pkg/audio/decode/opus.go

@@ -0,0 +1,52 @@
+// ABOUTME: Opus audio decoder
+// ABOUTME: Decodes Opus audio to int32 samples
+package decode
+
+import (
+	"fmt"
+
+	"github.com/Sendspin/sendspin-go/pkg/audio"
+	"gopkg.in/hraban/opus.v2"
+)
+
+type OpusDecoder struct {
+	decoder  *opus.Decoder
+	format   audio.Format
+	pcm16Buf []int16 // reusable decode buffer to avoid per-frame allocation
+}
+
+func NewOpus(format audio.Format) (Decoder, error) {
+	if format.Codec != "opus" {
+		return nil, fmt.Errorf("invalid codec for Opus decoder: %s", format.Codec)
+	}
+
+	dec, err := opus.NewDecoder(format.SampleRate, format.Channels)
+	if err != nil {
+		return nil, fmt.Errorf("failed to create opus decoder: %w", err)
+	}
+
+	return &OpusDecoder{
+		decoder:  dec,
+		format:   format,
+		pcm16Buf: make([]int16, 5760*format.Channels),
+	}, nil
+}
+
+func (d *OpusDecoder) Decode(data []byte) ([]int32, error) {
+	// Reuse pre-allocated int16 buffer for decode (avoids 23KB alloc per frame)
+	n, err := d.decoder.Decode(data, d.pcm16Buf)
+	if err != nil {
+		return nil, fmt.Errorf("opus decode failed: %w", err)
+	}
+
+	actualSamples := n * d.format.Channels
+	pcm32 := make([]int32, actualSamples)
+	for i := 0; i < actualSamples; i++ {
+		pcm32[i] = audio.SampleFromInt16(d.pcm16Buf[i])
+	}
+	return pcm32, nil
+}
+
+func (d *OpusDecoder) Close() error {
+	return nil
+}