add validated audio interleaving

internal/output/audio.go

@@ -0,0 +1,65 @@
+package output
+
+import (
+	"errors"
+
+	"mxl-player/internal/playback"
+)
+
+var (
+	ErrInvalidAudioFrame    = errors.New("invalid audio frame")
+	ErrAudioPayloadTooSmall = errors.New("audio channel payload is too small")
+)
+
+func InterleaveF32(frame playback.AudioFrame) ([]byte, error) {
+	if frame.Channels == 0 ||
+		frame.SampleCount == 0 ||
+		frame.SampleRateNumerator <= 0 ||
+		frame.SampleRateDenominator <= 0 {
+		return nil, ErrInvalidAudioFrame
+	}
+
+	if uint64(len(frame.Samples)) != frame.Channels {
+		return nil, ErrInvalidAudioFrame
+	}
+
+	if frame.SampleCount > ^uint64(0)/4 {
+		return nil, ErrInvalidAudioFrame
+	}
+	bytesPerChannel := frame.SampleCount * 4
+
+	if frame.Channels > ^uint64(0)/bytesPerChannel {
+		return nil, ErrInvalidAudioFrame
+	}
+	totalBytes := frame.Channels * bytesPerChannel
+
+	maxInt := uint64(^uint(0) >> 1)
+	if totalBytes > maxInt {
+		return nil, ErrInvalidAudioFrame
+	}
+
+	for _, samples := range frame.Samples {
+		if bytesPerChannel > uint64(len(samples)) {
+			return nil, ErrAudioPayloadTooSmall
+		}
+	}
+
+	result := make([]byte, int(totalBytes))
+
+	for sample := uint64(0); sample < frame.SampleCount; sample++ {
+		for channel := uint64(0); channel < frame.Channels; channel++ {
+			sourceOffset := sample * 4
+			destinationOffset := (sample*frame.Channels + channel) * 4
+
+			sourceStart := int(sourceOffset)
+			destinationStart := int(destinationOffset)
+
+			copy(
+				result[destinationStart:destinationStart+4],
+				frame.Samples[channel][sourceStart:sourceStart+4],
+			)
+		}
+	}
+
+	return result, nil
+}