add g711 utilities

README.md

@@ -19,10 +19,11 @@ Definitions and functions shared between [gortsplib](https://github.com/bluenvir
 |ISO 13818-2, Generic Coding of Moving Pictures and Associated Audio information, Part 2, Video|codecs / MPEG-1/2 Video|
 |ISO 14496-2, Coding of audio-visual objects, Part 2, Visual|codecs / MPEG-4 Video|
 |[ITU-T Rec. T-871, JPEG File Interchange Format](https://www.itu.int/rec/dologin_pub.asp?lang=e&id=T-REC-T.871-201105-I!!PDF-E&type=items)|codecs / JPEG|
-|[ITU-T Rec. H.264 (08/2021)](https://www.itu.int/rec/dologin_pub.asp?lang=e&id=T-REC-H.264-202108-I!!PDF-E&type=items)|codecs / H264|
-|[ITU-T Rec. H.265 (08/2021)](https://www.itu.int/rec/dologin_pub.asp?lang=e&id=T-REC-H.265-202108-I!!PDF-E&type=items)|codecs / H265|
+|[ITU-T Rec. H.264 (08/2021)](https://www.itu.int/rec/T-REC-H.264)|codecs / H264|
+|[ITU-T Rec. H.265 (08/2021)](https://www.itu.int/rec/T-REC-H.265)|codecs / H265|
 |[VP9 Bitstream & Decoding Process Specification v0.6](https://storage.googleapis.com/downloads.webmproject.org/docs/vp9/vp9-bitstream-specification-v0.6-20160331-draft.pdf)|codecs / VP9|
 |[AV1 Bitstream & Decoding Process](https://aomediacodec.github.io/av1-spec/av1-spec.pdf)|codecs / AV1|
+|[ITU-T Rec. G.711 (11/88)](https://www.itu.int/rec/T-REC-G.711)|codecs / G711|
 |ISO 11172-3, Coding of moving pictures and associated audio|codecs / MPEG-1/2 Audio|
 |ISO 13818-3, Generic Coding of Moving Pictures and Associated Audio information, Part 3, Audio|codecs / MPEG-1/2 Audio|
 |ISO 14496-3, Coding of audio-visual objects, Part 3, Audio|codecs / MPEG-4 Audio|

pkg/codecs/g711/decode.go

@@ -0,0 +1,61 @@
+// Package g711 contains utilities to work with the G711 codec.
+package g711
+
+var mulawTable = func() [256]uint16 {
+	var ret [256]uint16
+	for i := 0; i < 256; i++ {
+		v := ^i
+
+		tmp := (((uint16(v) & 0x0F) << 3) + 0x84) << ((v & 0x70) >> 4)
+
+		if (v & 0x80) != 0 {
+			ret[i] = 0x84 - tmp
+		} else {
+			ret[i] = tmp - 0x84
+		}
+	}
+	return ret
+}()
+
+var alawTable = func() [256]uint16 {
+	var ret [256]uint16
+	for i := 0; i < 256; i++ {
+		v := i ^ 0x55
+
+		t := uint16(v) & 0x0F
+		seg := (uint16(v) & 0x70) >> 4
+
+		if seg != 0 {
+			t = (t*2 + 1 + 32) << (seg + 2)
+		} else {
+			t = (t*2 + 1) << 3
+		}
+
+		if (v & 0x80) != 0 {
+			ret[i] = t
+		} else {
+			ret[i] = -t
+		}
+	}
+	return ret
+}()
+
+// DecodeMulaw decodes 8-bit G711 samples (MU-law) into 16-bit LPCM samples.
+func DecodeMulaw(in []byte) []byte {
+	out := make([]byte, len(in)*2)
+	for i, sample := range in {
+		out[i*2] = uint8(mulawTable[sample] >> 8)
+		out[(i*2)+1] = uint8(mulawTable[sample])
+	}
+	return out
+}
+
+// DecodeAlaw decodes 8-bit G711 samples (A-law) into 16-bit LPCM samples.
+func DecodeAlaw(in []byte) []byte {
+	out := make([]byte, len(in)*2)
+	for i, sample := range in {
+		out[i*2] = uint8(alawTable[sample] >> 8)
+		out[(i*2)+1] = uint8(alawTable[sample])
+	}
+	return out
+}

pkg/codecs/g711/decode_test.go

@@ -0,0 +1,27 @@
+package g711
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestDecodeMuLaw(t *testing.T) {
+	require.Equal(t,
+		DecodeMulaw([]byte{1, 2, 3, 255, 254, 253}),
+		[]byte{
+			0x86, 0x84, 0x8a, 0x84, 0x8e, 0x84, 0x00, 0x00,
+			0x00, 0x08, 0x00, 0x10,
+		},
+	)
+}
+
+func TestDecodeALaw(t *testing.T) {
+	require.Equal(t,
+		DecodeAlaw([]byte{1, 2, 3, 255, 254, 253}),
+		[]byte{
+			0xeb, 0x80, 0xe8, 0x80, 0xe9, 0x80, 0x03, 0x50,
+			0x03, 0x70, 0x03, 0x10,
+		},
+	)
+}