Application Layer: Video Streaming

Question 1

Video

Answer 1

Sequence of images displayed at constant rate

Question 2

Digital Image

Answer 2

Array of pixels represented by bits

Question 3

Video/Image Coding

Answer 3

Use redundancy within and between images to reduce # of bits used to encode images. Only change needed pixels

Question 4

Types of Multimedia Video

Answer 4

1. CBR
2. VBR

Question 5

CBR

Answer 5

Constant bit rate, video encoding rate fixed

Question 6

VBR

Answer 6

Variable bit rate, video encoding rate changes to adjust the number of bits used for different parts of a file

Question 7

Streaming

Answer 7

At same time, client playing out earlier part of video while server still sending out later part of video

Question 8

Continuous Playout Constraint

Answer 8

Challenge of streaming stored video. Once client playout begins, playback must match original timing.

Question 9

Client-side buffering and playout delay

Answer 9

Compensate for network-added delay, delay jitter

Question 10

DASH

Answer 10

Dynamic, Adaptive Streaming over HTTP

Question 11

DASH, Server-side

Answer 11

• divides video file into multiple chunks
• each chunk stored, encoded at different rates
• provide manifest file

Question 12

Manifest File

Answer 12

Provides URLs for different chunks

Question 13

DASH, Client-side

Answer 13

• periodically measures server-to-client bandwidth
• use manifest to request one chunk at a time

Question 14

DASH, Intelligence at client

Answer 14

Client determines:
- when to request chunk
- what encoding rate to request
- where to request chunk

Question 15

Streaming video equation

Answer 15

Streaming video = encoding + DASH + playout buffering

Question 16

CDN

Answer 16

Content Distribution Network, store/serve multiple copies of videos at multiple CDN nodes (geographically distributed sites)

Question 17

CDN Example

Answer 17

1. user visits netcinema web page and clicks on link for kingcdn video
2. user sends DNS query for video link
3. local DNS sends query to authoritative DNS server for netcinema
4. query gets sent to kingcdn private DNS infrastructure
5. user receives IP address of content serving CDN node
6. user makes TCP connection with CDN node and uses HTTP to get video
7. user receives manifest file

Question 18

Netflix example

Answer 18

1. log-in to netflix using netflix server
2. browse cloud for video and choose a video
3. get manifest file for video
4. copies of the video were previously uploaded to CDN servers
5. use manifest to request video chunks from specific CDN servers