move pkg/mpeg4audio into pkg/codecs/mpeg4audio

pkg/codecs/mpeg4audio/samplerates.go

@@ -0,0 +1,33 @@
+package mpeg4audio
+
+var sampleRates = []int{
+	96000,
+	88200,
+	64000,
+	48000,
+	44100,
+	32000,
+	24000,
+	22050,
+	16000,
+	12000,
+	11025,
+	8000,
+	7350,
+}
+
+var reverseSampleRates = map[int]int{
+	96000: 0,
+	88200: 1,
+	64000: 2,
+	48000: 3,
+	44100: 4,
+	32000: 5,
+	24000: 6,
+	22050: 7,
+	16000: 8,
+	12000: 9,
+	11025: 10,
+	8000:  11,
+	7350:  12,
+}