Rewrite HomeKit client

pkg/aac/aac.go

@@ -10,16 +10,18 @@ import (
 
 const (
 	TypeAACMain = 1
-	TypeAACLC   = 2
+	TypeAACLC   = 2  // Low Complexity
+	TypeAACLD   = 23 // Low Delay (48000, 44100, 32000, 24000, 22050)
 	TypeESCAPE  = 31
+	TypeAACELD  = 39 // Enhanced Low Delay
 
 	AUTime = 1024
+
+	// FMTP streamtype=5 - audio stream
+	FMTP = "streamtype=5;profile-level-id=1;mode=AAC-hbr;sizelength=13;indexlength=3;indexdeltalength=3;config="
 )
 
-// streamtype=5 - audio stream
-const fmtp = "streamtype=5;profile-level-id=1;mode=AAC-hbr;sizelength=13;indexlength=3;indexdeltalength=3;config="
-
-var sampleRates = []uint32{
+var sampleRates = [16]uint32{
 	96000, 88200, 64000, 48000, 44100, 32000, 24000, 22050, 16000, 12000, 11025, 8000, 7350,
 	0, 0, 0, // protection from request sampleRates[15]
 }
@@ -29,7 +31,7 @@ func ConfigToCodec(conf []byte) *core.Codec {
 	rd := bits.NewReader(conf)
 
 	codec := &core.Codec{
-		FmtpLine:    fmtp + hex.EncodeToString(conf),
+		FmtpLine:    FMTP + hex.EncodeToString(conf),
 		PayloadType: core.PayloadTypeRAW,
 	}
 
@@ -39,7 +41,7 @@ func ConfigToCodec(conf []byte) *core.Codec {
 	}
 
 	switch objType {
-	case TypeAACLC:
+	case TypeAACLC, TypeAACLD, TypeAACELD:
 		codec.Name = core.CodecAAC
 	default:
 		codec.Name = fmt.Sprintf("AAC-%X", objType)
@@ -72,3 +74,51 @@ func DecodeConfig(b []byte) (objType, sampleFreqIdx, channels byte, sampleRate u
 	channels = rd.ReadBits8(4)
 	return
 }
+
+func EncodeConfig(objType byte, sampleRate uint32, channels byte, shortFrame bool) []byte {
+	wr := bits.NewWriter(nil)
+
+	if objType < TypeESCAPE {
+		wr.WriteBits8(objType, 5)
+	} else {
+		wr.WriteBits8(TypeESCAPE, 5)
+		wr.WriteBits8(objType-32, 6)
+	}
+
+	i := indexUint32(sampleRates[:], sampleRate)
+	if i >= 0 {
+		wr.WriteBits8(byte(i), 4)
+	} else {
+		wr.WriteBits8(0xF, 4)
+		wr.WriteBits(sampleRate, 24)
+	}
+
+	wr.WriteBits8(channels, 4)
+
+	switch objType {
+	case TypeAACLD:
+		// https://github.com/FFmpeg/FFmpeg/blob/67d392b97941bb51fb7af3a3c9387f5ab895fa46/libavcodec/aacdec_template.c#L841
+		wr.WriteBool(shortFrame)
+		wr.WriteBit(0)      // dependsOnCoreCoder
+		wr.WriteBit(0)      // extension_flag
+		wr.WriteBits8(0, 2) // ep_config
+	case TypeAACELD:
+		// https://github.com/FFmpeg/FFmpeg/blob/67d392b97941bb51fb7af3a3c9387f5ab895fa46/libavcodec/aacdec_template.c#L922
+		wr.WriteBool(shortFrame)
+		wr.WriteBits8(0, 3) // res_flags
+		wr.WriteBit(0)      // ldSbrPresentFlag
+		wr.WriteBits8(0, 4) // ELDEXT_TERM
+		wr.WriteBits8(0, 2) // ep_config
+	}
+
+	return wr.Bytes()
+}
+
+func indexUint32(s []uint32, v uint32) int {
+	for i := range s {
+		if v == s[i] {
+			return i
+		}
+	}
+	return -1
+}

pkg/aac/aac_test.go

@@ -4,9 +4,25 @@ import (
 	"encoding/hex"
 	"testing"
 
+	"github.com/AlexxIT/go2rtc/pkg/core"
 	"github.com/stretchr/testify/require"
 )
 
+func TestConfigToCodec(t *testing.T) {
+	s := "profile-level-id=1;mode=AAC-hbr;sizelength=13;indexlength=3;indexdeltalength=3;config=F8EC3000"
+	s = core.Between(s, "config=", ";")
+	src, err := hex.DecodeString(s)
+	require.Nil(t, err)
+
+	codec := ConfigToCodec(src)
+	require.Equal(t, core.CodecAAC, codec.Name)
+	require.Equal(t, uint32(24000), codec.ClockRate)
+	require.Equal(t, uint16(1), codec.Channels)
+
+	dst := EncodeConfig(TypeAACELD, 24000, 1, true)
+	require.Equal(t, src, dst)
+}
+
 func TestADTS(t *testing.T) {
 	// FFmpeg MPEG-TS AAC (one packet)
 	s := "fff15080021ffc210049900219002380fff15080021ffc212049900219002380" //...

pkg/aac/adts.go

@@ -51,7 +51,7 @@ func ADTSToCodec(b []byte) *core.Codec {
 		Name:      core.CodecAAC,
 		ClockRate: sampleRates[sampleRateIdx],
 		Channels:  channels,
-		FmtpLine:  fmtp + hex.EncodeToString(conf),
+		FmtpLine:  FMTP + hex.EncodeToString(conf),
 	}
 	return codec
 }