Add muxer

astits/main.go

@@ -347,9 +347,9 @@ type Program struct {
 
 // Stream represents a stream
 type Stream struct {
-	Descriptors []string `json:"descriptors,omitempty"`
-	ID          uint16   `json:"id,omitempty"`
-	Type        uint8    `json:"type,omitempty"`
+	Descriptors []string          `json:"descriptors,omitempty"`
+	ID          uint16            `json:"id,omitempty"`
+	Type        astits.StreamType `json:"type,omitempty"`
 }
 
 func newProgram(id, mapID uint16) *Program {
@@ -359,7 +359,7 @@ func newProgram(id, mapID uint16) *Program {
 	}
 }
 
-func newStream(id uint16, _type uint8) *Stream {
+func newStream(id uint16, _type astits.StreamType) *Stream {
 	return &Stream{
 		ID:   id,
 		Type: _type,

crc32.go

@@ -0,0 +1,25 @@
+package astits
+
+const (
+	CRC32Polynomial = uint32(0xffffffff)
+)
+
+// computeCRC32 computes a CRC32
+// https://stackoverflow.com/questions/35034042/how-to-calculate-crc32-in-psi-si-packet
+func computeCRC32(bs []byte) uint32 {
+	return updateCRC32(CRC32Polynomial, bs)
+}
+
+func updateCRC32(crc32 uint32, bs []byte) uint32 {
+	for _, b := range bs {
+		for i := 0; i < 8; i++ {
+			if (crc32 >= uint32(0x80000000)) != (b >= uint8(0x80)) {
+				crc32 = (crc32 << 1) ^ 0x04C11DB7
+			} else {
+				crc32 = crc32 << 1
+			}
+			b <<= 1
+		}
+	}
+	return crc32
+}

data.go

@@ -8,10 +8,10 @@ import (
 
 // PIDs
 const (
-	PIDPAT  = 0x0    // Program Association Table (PAT) contains a directory listing of all Program Map Tables.
-	PIDCAT  = 0x1    // Conditional Access Table (CAT) contains a directory listing of all ITU-T Rec. H.222 entitlement management message streams used by Program Map Tables.
-	PIDTSDT = 0x2    // Transport Stream Description Table (TSDT) contains descriptors related to the overall transport stream
-	PIDNull = 0x1fff // Null Packet (used for fixed bandwidth padding)
+	PIDPAT  uint16 = 0x0    // Program Association Table (PAT) contains a directory listing of all Program Map Tables.
+	PIDCAT  uint16 = 0x1    // Conditional Access Table (CAT) contains a directory listing of all ITU-T Rec. H.222 entitlement management message streams used by Program Map Tables.
+	PIDTSDT uint16 = 0x2    // Transport Stream Description Table (TSDT) contains descriptors related to the overall transport stream
+	PIDNull uint16 = 0x1fff // Null Packet (used for fixed bandwidth padding)
 )
 
 // Data represents a data

data_eit.go

@@ -9,6 +9,7 @@ import (
 
 // EITData represents an EIT data
 // Page: 36 | Chapter: 5.2.4 | Link: https://www.dvb.org/resources/public/standards/a38_dvb-si_specification.pdf
+// (barbashov) the link above can be broken, alternative: https://dvb.org/wp-content/uploads/2019/12/a038_tm1217r37_en300468v1_17_1_-_rev-134_-_si_specification.pdf
 type EITData struct {
 	Events                   []*EITDataEvent
 	LastTableID              uint8

data_nit.go

@@ -8,6 +8,7 @@ import (
 
 // NITData represents a NIT data
 // Page: 29 | Chapter: 5.2.1 | Link: https://www.dvb.org/resources/public/standards/a38_dvb-si_specification.pdf
+// (barbashov) the link above can be broken, alternative: https://dvb.org/wp-content/uploads/2019/12/a038_tm1217r37_en300468v1_17_1_-_rev-134_-_si_specification.pdf
 type NITData struct {
 	NetworkDescriptors []*Descriptor
 	NetworkID          uint16

data_pat.go

@@ -6,6 +6,10 @@ import (
 	"github.com/asticode/go-astikit"
 )
 
+const (
+	PATSectionEntryBytesSize = 4 // 16 bits + 3 reserved + 13 bits = 32 bits
+)
+
 // PATData represents a PAT data
 // https://en.wikipedia.org/wiki/Program-specific_information
 type PATData struct {
@@ -41,3 +45,19 @@ func parsePATSection(i *astikit.BytesIterator, offsetSectionsEnd int, tableIDExt
 	}
 	return
 }
+
+func calcPATSectionLength(d *PATData) uint16 {
+	return uint16(4 * len(d.Programs))
+}
+
+func writePATSection(w *astikit.BitsWriter, d *PATData) (int, error) {
+	b := astikit.NewBitsWriterBatch(w)
+
+	for _, p := range d.Programs {
+		b.Write(p.ProgramNumber)
+		b.WriteN(uint8(0xff), 3)
+		b.WriteN(p.ProgramMapID, 13)
+	}
+
+	return len(d.Programs) * PATSectionEntryBytesSize, b.Err()
+}

data_pat_test.go

@@ -34,3 +34,13 @@ func TestParsePATSection(t *testing.T) {
 	assert.Equal(t, d, pat)
 	assert.NoError(t, err)
 }
+
+func TestWritePatSection(t *testing.T) {
+	bw := &bytes.Buffer{}
+	w := astikit.NewBitsWriter(astikit.BitsWriterOptions{Writer: bw})
+	n, err := writePATSection(w, pat)
+	assert.NoError(t, err)
+	assert.Equal(t, n, 8)
+	assert.Equal(t, n, bw.Len())
+	assert.Equal(t, patBytes(), bw.Bytes())
+}