chore: establish local platform baseline

internal/media/validation.go

@@ -0,0 +1,47 @@
+package media
+
+import "encoding/binary"
+
+func validateAudio(codec string, declaredDurationMS int, prefix []byte) string {
+	if codec != "wav_pcm_s16le" {
+		return "CODEC_VALIDATION_UNAVAILABLE"
+	}
+	if len(prefix) < 44 || string(prefix[:4]) != "RIFF" || string(prefix[8:12]) != "WAVE" {
+		return "INVALID_AUDIO_CONTAINER"
+	}
+	var byteRate, dataSize uint32
+	var audioFormat, bitsPerSample uint16
+	for offset := 12; offset+8 <= len(prefix); {
+		chunkID := string(prefix[offset : offset+4])
+		chunkSize := int(binary.LittleEndian.Uint32(prefix[offset+4 : offset+8]))
+		dataStart := offset + 8
+		if chunkID == "data" {
+			dataSize = uint32(chunkSize)
+			break
+		}
+		if chunkSize < 0 || dataStart+chunkSize > len(prefix) {
+			break
+		}
+		switch chunkID {
+		case "fmt ":
+			if chunkSize < 16 {
+				return "INVALID_AUDIO_CONTAINER"
+			}
+			audioFormat = binary.LittleEndian.Uint16(prefix[dataStart : dataStart+2])
+			byteRate = binary.LittleEndian.Uint32(prefix[dataStart+8 : dataStart+12])
+			bitsPerSample = binary.LittleEndian.Uint16(prefix[dataStart+14 : dataStart+16])
+		}
+		offset = dataStart + chunkSize
+		if offset%2 != 0 {
+			offset++
+		}
+	}
+	if audioFormat != 1 || bitsPerSample != 16 || byteRate == 0 || dataSize == 0 {
+		return "UNSUPPORTED_AUDIO_ENCODING"
+	}
+	actualDurationMS := int((uint64(dataSize) * 1000) / uint64(byteRate))
+	if actualDurationMS != declaredDurationMS {
+		return "DURATION_MISMATCH"
+	}
+	return ""
+}