Documentation
¶
Overview ¶
Package mpegts implements encoding and decoding of MPEG-TS packets as specified in ITU-T H.222.0.
Example ¶
The most common usage of mpegts involves the use of Scanner which steps through the packets of a transport stream. In this example we decode then re-encode every packet from the standard input to the standard output. If a packet contains a clock reference, we print that out to the standard error for diagnostics. This provides similar functionality to the following ffprobe command:
ffprobe -show_packets -
package main
import (
"fmt"
"log"
"os"
"github.com/untangledco/streaming/mpegts"
)
func main() {
sc := mpegts.NewScanner(os.Stdin)
var i int
for sc.Scan() {
i++
packet := sc.Packet()
if packet.Adaptation != nil && packet.Adaptation.PCR != nil {
ticks := packet.Adaptation.PCR.Ticks()
fmt.Fprintf(os.Stderr, "packet %d\t%d\n", i, ticks)
}
if err := mpegts.Encode(os.Stdout, packet); err != nil {
log.Printf("encode packet %d: %v", i, err)
}
}
if sc.Err() != nil {
log.Fatalf("scan: %v", sc.Err())
}
}
Output:
Index ¶
Examples ¶
Constants ¶
const ( FieldPTS uint8 = 1 << (7 - iota) FieldDTS FieldESCR FieldESRate FieldTrickMode FieldCopyInfo FieldCRC FieldExtension )
Flags indicating which optional fields are present in a PES header's payload.
const PacketSize int = 188
PacketSize is the length of a MPEG-TS packet in bytes.
const Sync byte = 'G'
Sync is the first byte of a MPEG-TS packet.
Variables ¶
var ErrLongPacket = errors.New("long packet")
var ErrShortPacket = errors.New("short packet")
Functions ¶
Types ¶
type Adaptation ¶
type Adaptation struct {
// If true, there is a discontinuity between this packet and
// either the continuity conter or PCR.
Discontinuous bool
// If true, the packet may be used as an index from which to
// randomly access other points in the stream.
RandomAccess bool
// Whether this stream is high priority.
Priority bool
SpliceCountdownSet bool
PCR *PCR
// Original program clock reference.
OPCR *PCR
// The number of packets remaining until a splicing point.
SpliceCountdown uint8
// Raw bytes of any application-specific data.
Private []byte
// Raw bytes of the adaptation extension field.
Extension []byte
// A slice of bytes all with the value 0xff; enough to ensure
// a packet's length is always PacketSize.
Stuffing []byte
}
Adaptation represents an adaptation field including the header.
type PCR ¶
type PCR struct {
// 33-bit integer holding the number of ticks of a 90KHz clock.
Base uint64
// 9-bit integer holding 27MHz ticks, intended as a
// constant addition to Base.
Extension uint16
}
PCR represents a Program Clock Reference.
type PESHeader ¶
type PESHeader struct {
// Scrambling informs decoders how packet contents are encrypted or "scrambled".
// Zero indicates the stream is not scrambled.
Scrambling uint8
// Priority signals to decoders that this packet should be processed before others.
Priority bool
// Alignment indicates thatheader is immediately followed by
// the video start code or audio syncword.
Alignment bool
// Copyrighted signals that stream's content is copyrighted.
Copyrighted bool
// Original signals whether the stream is an original or copy.
Original bool
// Fields indicates which optional fields are present in Optional.
Fields uint8
Presentation *Timestamp
Decode *Timestamp
// Optional holds any bytes that we don't know how to decode (yet).
// TOOD(otl): also contains stuffing bytes, which should be stored separately.
Optional []byte
}
PESHeader represents the optional header of a PES packet.
type PESPacket ¶
type PESPacket struct {
// ID uniquely identifies this stream from other elementary streams.
ID byte
// Length is the number of bytes for this packet.
// A value of zero indicates the packet can be of any length,
// but is only valid when the underlying stream is video.
Length uint16
Header *PESHeader
// Data contains raw audio/video data.
Data []byte
}
PESPacket represents a packetised elementary stream (PES) packet. These are transported in MPEG-TS packet payloads.
type Packet ¶
type Packet struct {
// If true, the packet should be discarded.
Error bool
// Indicates whether the payload holds the first byte of a particular payload such as ... TODO(otl)
PayloadStart bool
// If true, this packet has higher priority than other packets
// with the same PID.
Priority bool
// Identifies the type of the packet.
PID PacketID
// Specifies which algorithm, if any, is used to encrypt the payload.
Scrambling Scramble
Continuity uint8
Adaptation *Adaptation
PES *PESPacket
// Payload contains the raw bytes of any payload we do not support decoding.
Payload []byte
// contains filtered or unexported fields
}
type Timestamp ¶
type Timestamp struct {
// PTS indicates the packet carrying the timestamp contains a presentation timestamp.
PTS bool
// DTS indicates the packet carrying this timestamp contains a decode timestamp.
DTS bool
// Ticks holds a 33-bit integer counting the number of ticks of a 90KHz clock.
Ticks uint64
}
Timestamp represents the timestamp transported in a PES packet header. It is used by decoders to reliably time and synchronise playback of video/audio payloads.
Source Files