Πολυμεσικό Υλικό στο Internet: Συγχρ - PowerPoint Presentation

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Πολυμεσικό Υλικό στο Internet: Συγχρ - PPT Presentation

Διακίνηση Διακίνηση Video με χρήση του HTTP 8 1201 5 Β Μάγκλαρης ltmaglarisnetmodentuagrgt Μ Γραμματικού lt marynetmodentuagr ID: 156847

http video player streaming video http streaming player media rtsp file netflix tcp time audio server adaptive chunks web

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Slide1

Πολυμεσικό Υλικό στο Internet: Συγχρονισμός, Επεξεργασία και ΔιακίνησηΔιακίνηση Video με χρήση του HTTP8/1/2015

Β. Μάγκλαρης

<maglaris@netmode.ntua.gr>

Μ. Γραμματικού

mary@netmode.ntua.gr

Δ.

Καλογεράς

<dkalo@noc.ntua.ge>

www.netmode.ntua.gr

Slide2

OutlineStreaming over Internet1st Generation Progressive2nd Generation

UDP based Real-Time

Protocols

(RTP,

RTCP, RTSP

)

Generation

TCP based

Proprietary – Adobe

Adaptive HTTP basedSlide3

ChallengesTCP/UDP/IP , best-effort, with no guarantees on expectation or variance of packet delayStreaming applications delay of 5 to 10 seconds is typical and has been acceptable, but performance deteriorate if links are congested

Real

-Time Interactive requirements on delay and its jitter have been satisfied by over-provisioning (providing plenty of bandwidth), what will happen when the load increases?...Slide4

On-Demand

Streaming

Important and growing application due to reduction of storage costs, increase in high speed net access from homes, enhancements to caching

Interactive control by user

(but often with long response time)

Ubiquitous on the web:

YouTube, Netflix,

Vimeo

Television networks, Hollywood, etc.

Most local radio & TV stations

Virtually everywhere on websitesSlide5

First Generation: HTTP Download

A simple architecture is to have the Browser request the object(s) and after their reception pass them to the player

for display

No pipeliningSlide6

Helper Application – i.e. media playerDisplays content, which is typically requested via a Web browser; typical functions:DecompressionJitter removalError correction: use redundant packets to be used for reconstruction of original stream

GUI for user control

Examples:

RealPlayer

Adobe Flash Player

Windows Media Player

QuickTimeDivX Web PlayerSlide7

First Gen: HTTP Progressive Download (2)Alternative: set up connection between server and player; player takes overWeb browser requests and receives a Meta File

(a file describing the object) instead of receiving the file itself;

Browser launches the appropriate Player and passes it the

Meta File

;

Player sets up a TCP connection with Web Server and downloads or

streams the fileSlide8

Meta file requestsSlide9

HTTP Progressive DownloadWith helper application doing the download, playback can start immediately...Or after sufficient bytes are bufferedSender sends at maximum possible rate under TCP; retransmit when error is encountered; Player uses a much larger buffer to smooth delivery rate of TCPSlide10

HTTP Progressive DownloadSlide11

Buffering Continuous MediaJitter = variation from ideal timingMedia delivery must have very low jitter Video frames every 30ms or soAudio: ultimately samples need < 128ms

jitter

But network packets have much more jitter that that!

Solution: buffers

Fill them with best effort

Drain them via low-latency, local access Slide12

Streaming, Buffers and Timing

Time

Max Buffer Duration

= allowable jitter

File Position

Max Buffer Size

Smooth Playback Time

Buffer almost empty

"Good" Region:

smooth playback

"Bad": Buffer underflows and

playback stops

"Bad": Buffer overrflows

Buffer

Duration

Buffer

SizeSlide13

The myth of SBRAny single bitrate you choose for a video is by definition the wrong video for 99% of users.

These users will

rebuffer

These have lower quality than they could

sustainSlide14

Drawbacks of HTTP Progressive Download (2)HTTP connection keeps data flowing as fast as possible to user's local bufferMay download lots of extra data if you do not watch the videoTCP file transfer can use more bandwidth than necessary

Mismatch between whole file transfer and stop/start/seek playback controls.

However: use file range requests to seek to video position

Cannot change video quality (bit rate) to adapt to network congestion Slide15

2nd Generation: Real-Time StreamingThis gets us around HTTP, allows a choice of UDP vs. TCP and the application layer protocol can be better tailored to Streaming; many enhancements options are possibleSlide16

RTSP and RTP

Legacy Video Streaming ApproachesSlide17

Example: Real Time Streaming Protocol (RTSP)For user to control display: rewind, fast forward, pause, resume, etc…Out-of-band protocol (uses two connections, one for control messages (Port 554) and one for media stream)RFC 2326 permits use of either TCP or UDP for the control messages connection, sometimes called the RTSP ChannelAs before, meta file is communicated to web browser which then launches the Player; Player sets up an RTSP connection for control messages in addition to the connection for the streaming mediaSlide18

RTSP OperationSlide19

RTSP Media Stream

Stateful

Server keeps track of client's state

Client issues Play, Pause, ..., Close

Steady stream of packets

UDP - lower latency

TCP - may get through more firewalls, reliable

Credit: some content adapted from Alex ZambelliSlide20

RTSP Exchange Example

C: SETUP rtsp://audio.example.com/xena/audio RTSP/1.0

Transport:

rtp

udp

; compression; port=3056; mode=PLAY

S: RTSP/1.0 200 1 OK

Session 4231

C: PLAY rtsp://audio.example.com/xena/audio.en/lofi RTSP/1.0

Session: 4231

Range:

npt

=0 (

npt

= normal play time)

C: PAUSE rtsp://audio.example.com/xena/audio.en/lofi RTSP/1.0

Session: 4231

Range:

npt

=37

C: TEARDOWN rtsp://audio.example.com/xena/audio.en/lofi RTSP/1.0

Session: 4231

S: 200 3 OKSlide21

Example 2: RTMP

- Real-Time Messaging Protocol

Proprietary Adobe protocol

Runs over TCP

Manages audio, video, and other

Multiplex multiple streams over TCP connectionSlide22

Flash Streaming ServerFlash Streaming Server communicates with its clients using the Adobe patented RTMP over TCP, which manages a two-way connection, allowing the server to send and receive,video, audio and

data between client and server

Typically used with FLV encoded filesSlide23

Variations of RTMPRTMP- Standard,unencrypted RTMP.

The default port is 1935.

RTMPT-

RTMP “tunneled” over HTTP

The default port is 80

RTMPS- RTMP sent over an SSL. SSL enables secure

TCP/IP connections. The default port is 443RTMPE- Enhanced and encrypted version of RTMP.

RTMPTE- Encrypts the communication channel, tunneling over HTTPSlide24

Drawbacks of RTSP, RTMP

Web downloads are typically cheaper than streaming services offered by CDNs and hosting providers

Streaming often blocked by routers

UDP itself often blocked by firewalls

HTTP delivery can use ordinary proxies and caches

Conclusion: rather than adapt Internet to streaming, adapt media delivery to the InternetSlide25

Bandwidth is never constantEven preselecting bitrates will lead to rebuffering problems as bandwidth fluctuates over the duration of the vide, especially for long form contentIdeally we would like to switch bitrates constantly to always give the user the highest quality they can sustain at any point in time.

BufferingSlide26

Buffering

500kbps

1000kbps

1500kbps

Adaptive deliverySlide27

3rd Generation: HTTP StreamingOther terms for similar concepts: Adaptive Streaming, Smooth Streaming, HTTP ChunkingClient-centric architecture with stateful client and stateless server Standard server: Web serversStandard Protocol: HTTP

Session state and logic maintained at server

Video is broken into multiple chunks

Chunks begin with

keyframe

so independent of other chunks

A series of HTTP progressive downloads of chunksPlaying chunks in sequence gives seamless videoSlide28

Adaptive Bit Rate with HTTP Streaming Encode video at different levels of quality/bandwidthClient can adapt by requesting different sized chunksChunks of different bit rates must be

synchronized

All

encodings have the same chunk boundaries and all chunks start with

keyframes

, so you can make smooth splices to chunks of higher or lower bit

ratesSlide29

How does segmentation work?

Incoming video

into multiple short blocks. Each block holds the same section of video, encoded at a different size and bitrate.

500 kbps

2000 kbps

1000 kbps

is split by an

encoder

2Slide30

How does adaptive delivery work?

The segmented video is stored on a server, along with a text file which describes the names of each segment. This text file is called a

manifest

A player downloads the manifest and then begins requesting individual segments of video.

It makes its choice based on bandwidth conditions, grabbing the best quality it can at the time.

SERVER

CLOUD

PLAYERSlide31

Media Source Extension – the future of browser videoA W3C standard - https://dvcs.w3.org/hg/html-media/raw-file/tip/media-source/media-source.html Supported today by Chrome, IE11 and Opera

MSE allows JavaScript to

fetch and parse a manifest

etrieve video, audio and text segments using XHR

eed them to the <video> tag to be decoded and rendered.

MSE gives developers incredible control over playback,

buffering and adaption logic of in-page video.Slide32

Pareto principle in video popularityAlso known as the “80-20” (or 90-10) rule [http://en.wikipedia.org/wiki/Pareto_principle]Associated with highly skewed distributions

Caused by positive-feedback effects (“the rich get richer”)

Does non-UGC content (say movies from

NetFlix

) follow a similar pattern?

A practical implication of this

skewness: caching applies!Slide33

Caching works…Let’s build CDNsTake advantage of locality and relativityA practical implication of this skewness: caching works

Akamai

You tube

Netflix based on Amazon

infrastractureSlide34

Adaptive HTTP Streaming System (Protocol)ServerCan be standard web serverMedia segment can be prepared in-line or off-line

Client

Sends series of HTTP GET segment requests and receives segments

Performs rate adaptation before sending a new GET segment requestSlide35

Advantages of HTTP Streaming

Easy to deploy: it's just HTTP, work with

existing

caches/proxies/CDN/Firewall

Fast startup by downloading lowest quality/smallest chunk

Bitrate switching is seamless

Many small files

Small with respect to the movie size

Large with respect to TCP

5-10 seconds of 1Mbps – 3Mbps

 0.5MB – 4MB per chunkSlide36

Which adaptive streaming formats exist today?HTTP Live Streaming (HLS)

Controlled by Apple

Known as HLS, it is supported well by

iOS

, Safari and half-heartedly by Android.

HTTP Dynamic Streaming (HDS)

Controlled by AdobeKnown as HDS, it is played back only by Flash clients with custom apps.Smooth Streaming (SMOOTH)Controlled by Microsoft

Played back via Silverlight clients, Xbox, MPEG-DASH (DASH)

An ISO standard

Playback via MSE in browsers, native apps on

iOS

, Android and

WInOS

. Slide37

Simple HLS example <video id="player" controls poster="sintel.jpg" preload="none" style="width:480px;height:204px"> <source src="

http://multiplatform-

f.akamaihd.net

/multi/april11/

sintel/sintel-hd_,512x288_450_b,640x360_700_b,768x432_1000_b,.mp4.csmil/master.m3u8" type='application/x-mpegURL' /> <source src

="http://akamaicorp-pmd.edgesuite.net/flashvod

/video/mp4/sintel.mp4" type='video/mp4'/>

<source

src

="http://

akamaicorp-pmd.edgesuite.net

flashvod

/video/mp4/

sintel.webm

" type='video/

webm

' />

</video>Slide38

Example of HLS Meta Data Slide39

RTMP

Πολυμεσικό Υλικό στο Internet: Συγχρ - PowerPoint Presentation

Πολυμεσικό Υλικό στο Internet: Συγχρ - PPT Presentation

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