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MPEG + RTP
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Previously, on CS5248 MPEG Compression
Sequence, GOP, Picture, Slice, Macroblock, Block, DC/AC Coefficient I-Frame, P-Frame, B-Frame NUS.SOC.CS5248 Ooi Wei Tsang
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Previously, on CS5248 RTP headers
SSRC, Media Timestamp, Marker Bit, Payload Type .. Application-Level Framing NUS.SOC.CS5248 Ooi Wei Tsang
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You are Here Encoder Decoder Middlebox Sender Receiver Network
NUS.SOC.CS5248 Ooi Wei Tsang
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Application-Level Framing
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Let the application decide, not protocol stacks.
How to send/recv? Let the application decide, not protocol stacks. Tennenhouse + Clark NUS.SOC.CS5248 Ooi Wei Tsang
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Application Knows Best
How to reorder packets Whether to ignore loss Which packet to retransmit NUS.SOC.CS5248 Ooi Wei Tsang
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Application Data Unit (ADU)
Can be processed individually, even out-of-order 8-Bit PCM audio: 1 ADU = 1 Byte MPEG1 Video: 1 ADU = NUS.SOC.CS5248 Ooi Wei Tsang
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How to chop data into packets?
Every received packet should be useful (even in very lossy environment) Ideally, 1 ADU in 1 packet NUS.SOC.CS5248 Ooi Wei Tsang
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RTP Payload Header MPEG-1? 2? Temporal Reference I? P? B?
RTP Header RTP Payload Header RTP Payload MPEG-1? 2? Temporal Reference I? P? B? Begin of Slice? End of Slice? NUS.SOC.CS5248 Ooi Wei Tsang
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RTP Header Media Timestamp: 32 bits
the instant the first byte in this packet is captured 90 kHz timestamp (90000 = 1 second) NUS.SOC.CS5248 Ooi Wei Tsang
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RTP Header Marker Bit: 1 if contains the last byte of a frame
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RTP Header 32 for MPEG-1 Payload Type: 7 bits NUS.SOC.CS5248
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RTP Payload Header MBZ (5 bits) Unused. Must be 0 NUS.SOC.CS5248
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RTP Payload Header T (1 bit)
1 if there is a MPEG-2 Extension Header after this header. NUS.SOC.CS5248 Ooi Wei Tsang
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RTP Payload Header Temporal Reference (10 bits)
The ‘frame number’ of the current frame within the GOP NUS.SOC.CS5248 Ooi Wei Tsang
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RTP Payload Header AN bit and N bit Set to 0 for MPEG-1 NUS.SOC.CS5248
Ooi Wei Tsang
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RTP Payload Header S (1 bit)
Is there a sequence header in this packet? NUS.SOC.CS5248 Ooi Wei Tsang
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RTP Payload Header BS (1 bit) and ES (1bit)
BS is 1 iff the ‘first’ byte of this payload is a slice header ES is 1 iff the last byte of this payload is the end of a slice NUS.SOC.CS5248 Ooi Wei Tsang
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RTP Payload Header Picture Type (3 bits) I (1), P (2), B (3), D (4)
NUS.SOC.CS5248 Ooi Wei Tsang
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RTP Payload Header Motion Vectors Information
Get from most recent picture header NUS.SOC.CS5248 Ooi Wei Tsang
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Fragmentation Rules Sequence header: at the start of payload
GOP header: at the start of a payload (or follows Sequence header) Picture header: at the start of a payload (or follows Sequence/GOP header) NUS.SOC.CS5248 Ooi Wei Tsang
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Fragmentation Rules A slice must be either
First data in the packet, or Follows integral number of slices A slice may be fragmented if exceeds the size of a packet NUS.SOC.CS5248 Ooi Wei Tsang
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Packet Size 1 MTU is 1500 bytes IP Header UDP Header RTP Header
RTP Payload Header Payload Size = NUS.SOC.CS5248 Ooi Wei Tsang
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Packetize MPEG-1 Video into RTP Packets
Project 1 Packetize MPEG-1 Video into RTP Packets
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Goal Read MPEG-1 video, output RTP packets with proper: RTP headers
RTP payload headers fragmentation NUS.SOC.CS5248 Ooi Wei Tsang
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Mnt (Media Networking Toy)
C++ Tcl/OTcl UNIX NUS.SOC.CS5248 Ooi Wei Tsang
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Overview OTcl C++ MntData MntComponents NUS.SOC.CS5248 Ooi Wei Tsang
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MntComponent recv(MntData *data) push(MntData *data) NUS.SOC.CS5248
Ooi Wei Tsang
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MntPump Subclass of MntComponent No recv()
pump_some( ) { generate data push(data) pump_timer_.msched(time) } NUS.SOC.CS5248 Ooi Wei Tsang
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Create and Link Components
set a [new MntA] set b [new MntB] $a add_link_to $b $a instproc on_stop_pumping {} { puts “done!” exit } $a start_pumping vwait forever NUS.SOC.CS5248 Ooi Wei Tsang
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Important Classes MntComponent MntRTPFileWriter MntPump
MntRTPPayloadDumper MntRTPFileReader MntMPEGFileRTPizer NUS.SOC.CS5248 Ooi Wei Tsang
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Important Classes MntData MntRTPMPEGPacket MntRTPHdr
MntRTPMPEGHdr NUS.SOC.CS5248 Ooi Wei Tsang
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MntRTPMPEGPacket MntRTPHdr *rtp_hdr_; MntRTPMPEGHdr *pl_hdr_;
RTP Header RTP Payload Header RTP Payload MntRTPHdr *rtp_hdr_; MntRTPMPEGHdr *pl_hdr_; unsigned char *pl_data_; int pl_len_; NUS.SOC.CS5248 Ooi Wei Tsang
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Example Tcl Scripts
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Dealing with Bits BitStream A buffer buffer_ endDataPtr_ endBufPtr_
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Dealing with Bits BitParser Read bits from BitStream BitParser 1011101
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Basic Usage #include “mnt_bit_parser.h” #include “mnt_bit_stream.h”
BitStream *bs = new BitStream(“a.mpg”); BitParser *bp = new BitParser(); bp->wrap(bs); int x; Bp_GetInt(bp, x); NUS.SOC.CS5248 Ooi Wei Tsang
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Dealing with MPEG Headers
MntMPEG1SeqHdr MntMPEG1GopHdr MntMPEG1PicHdr MntMPEG1SliceHdr NUS.SOC.CS5248 Ooi Wei Tsang
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Basic Operations hdr->parse(bp) hdr->find(bp) hdr->skip(bp)
hdr->dump(bp1,bp2) NUS.SOC.CS5248 Ooi Wei Tsang
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Example: MPEG Parsing
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Project Homepage Descriptions Skeleton Code Mnt Documentation
IVLE Forums NUS.SOC.CS5248 Ooi Wei Tsang
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Advice Use the source wisely Start early NUS.SOC.CS5248 Ooi Wei Tsang
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