Download - MPEG + RTP

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Page 1: MPEG + RTP

NUS.SOC.CS5248-2009Roger Zimmermann (based in part on slides by Ooi Wei Tsang)

MPEG + RTP

Page 2: MPEG + RTP

NUS.SOC.CS5248-2009Roger Zimmermann (based in part on slides by Ooi Wei Tsang)

Previously, on CS5248

MPEG Compression Sequence, GOP, Picture, Slice,

Macroblock, Block, DC/AC Coefficient

I-Frame, P-Frame, B-Frame

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NUS.SOC.CS5248-2009Roger Zimmermann (based in part on slides by Ooi Wei Tsang)

MPEG Frame Sizes

Constant Bitrate (CBR) vs. Variable Bitrate (VBR)

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NUS.SOC.CS5248-2009Roger Zimmermann (based in part on slides by Ooi Wei Tsang)

Previously, on CS5248

RTP headers SSRC, Media Timestamp, Marker Bit,

Payload Type ..

Application-Level Framing

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NUS.SOC.CS5248-2009Roger Zimmermann (based in part on slides by Ooi Wei Tsang)

You are Here

Network

Encoder

Sender

Middlebox

Receiver

Decoder

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NUS.SOC.CS5248-2009Roger Zimmermann (based in part on slides by Ooi Wei Tsang)

Application-Level Framing

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NUS.SOC.CS5248-2009Roger Zimmermann (based in part on slides by Ooi Wei Tsang)

How to send/recv?

Let the application decide, not protocol

stacks.

Tennenhouse + Clark

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NUS.SOC.CS5248-2009Roger Zimmermann (based in part on slides by Ooi Wei Tsang)

Application Knows Best

How to reorder packetsWhether to ignore lossWhich packet to retransmit

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NUS.SOC.CS5248-2009Roger Zimmermann (based in part on slides by Ooi Wei Tsang)

Application Data Unit (ADU)

Can be processed individually, even out-of-order

Unit of error-recovery If part of an ADU is lost, the whole ADU

is considered lost

8-Bit PCM audio: 1 ADU = 1 ByteMPEG1 Video: 1 ADU =

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NUS.SOC.CS5248-2009Roger Zimmermann (based in part on slides by Ooi Wei Tsang)

How to chop data into packets?

Every received packet should be useful (even in very lossy environments)

Ideally, 1 ADU in 1 packet

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NUS.SOC.CS5248-2009Roger Zimmermann (based in part on slides by Ooi Wei Tsang)

RTP Payload Header

RTP HeaderRTP Payload

HeaderRTP Payload

•MPEG-1? 2?•Temporal Reference•I? P? B?•Begin of Slice? End of Slice?

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NUS.SOC.CS5248-2009Roger Zimmermann (based in part on slides by Ooi Wei Tsang)

RTP Header

Media Timestamp: 32 bits the instant the first byte in this packet is

captured 90 kHz timestamp (90000 = 1 second)

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NUS.SOC.CS5248-2009Roger Zimmermann (based in part on slides by Ooi Wei Tsang)

RTP Header

Marker Bit: 1 if contains the last byte of a frame

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NUS.SOC.CS5248-2009Roger Zimmermann (based in part on slides by Ooi Wei Tsang)

RTP Header

Payload Type: 7 bits 32 for MPEG-1

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NUS.SOC.CS5248-2009Roger Zimmermann (based in part on slides by Ooi Wei Tsang)

RTP Payload Header

MBZ (5 bits) Unused. Must be 0

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NUS.SOC.CS5248-2009Roger Zimmermann (based in part on slides by Ooi Wei Tsang)

RTP Payload Header

T (1 bit) 1 if there is a MPEG-2 Extension Header

after this header.

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NUS.SOC.CS5248-2009Roger Zimmermann (based in part on slides by Ooi Wei Tsang)

RTP Payload Header

Temporal Reference (10 bits) The ‘frame number’ of the current frame

within the GOP

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NUS.SOC.CS5248-2009Roger Zimmermann (based in part on slides by Ooi Wei Tsang)

RTP Payload Header

AN bit and N bit Set to 0 for MPEG-1

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NUS.SOC.CS5248-2009Roger Zimmermann (based in part on slides by Ooi Wei Tsang)

RTP Payload Header

S (1 bit) Is there a sequence header in this packet? Repetition of sequence header is useful for

resynchronization

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NUS.SOC.CS5248-2009Roger Zimmermann (based in part on slides by Ooi Wei Tsang)

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

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NUS.SOC.CS5248-2009Roger Zimmermann (based in part on slides by Ooi Wei Tsang)

RTP Payload Header

Picture Type (3 bits) I (1), P (2), B (3), D (4)

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NUS.SOC.CS5248-2009Roger Zimmermann (based in part on slides by Ooi Wei Tsang)

RTP Payload Header

Motion Vectors Information Get from most recent picture header

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NUS.SOC.CS5248-2009Roger Zimmermann (based in part on slides by Ooi Wei Tsang)

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)

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NUS.SOC.CS5248-2009Roger Zimmermann (based in part on slides by Ooi Wei Tsang)

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

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NUS.SOC.CS5248-2009Roger Zimmermann (based in part on slides by Ooi Wei Tsang)

Packet Size

1 MTU is 1500 bytes IP HeaderUDP HeaderRTP HeaderRTP Payload HeaderPayload Size =

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NUS.SOC.CS5248-2009Roger Zimmermann (based in part on slides by Ooi Wei Tsang)

Project

Packetize MP3 or Speex audio into RTP Packets

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NUS.SOC.CS5248-2009Roger Zimmermann (based in part on slides by Ooi Wei Tsang)

Goal

Use the Yima Personal Edition streaming media server code

Modify the yimasplit utility, which creates data blocks containing pre-computed RTP packets

Server reads data blocks and sends out RTP packets

Modify client to decompress and play audio

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NUS.SOC.CS5248-2009Roger Zimmermann (based in part on slides by Ooi Wei Tsang)

Project Homepage

DescriptionsYima Personal Edition Code on CD-

ROMDocumentation IVLE Forums

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NUS.SOC.CS5248-2009Roger Zimmermann (based in part on slides by Ooi Wei Tsang)

Advice

The Yima PE source code is not very well documented

Select your own project, or do the suggested one

Either way: Start early


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