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2023-09-26

Summary

keywords video streaming, CDN, pixel, frames/sec, spatial coding, temporal coding

TODO

HW read Chapter 5 5.6(data center), 5.7(A day in the life of a web page request) parts What is difference of compression and encoding?

Exercise* Should read these again..

Next time

Video Streaming

how can we scale to more users? heterogeneity : different capabilities on different users.

solution : distributed(CDN) , application-level infrastructure(DASH protocol)

What is a video?

sequence of images displayed at constant rate.

pixel : smallest unit in the image, stored in bits, storing color coding.

How can we decrease image bits?

  1. spatial : use redundancy within an image
  2. temporal: use redundancy between images

#todo :What is difference of compression and encoding?

video encoding​

find the resolution : 1920p * 1080p find bit each pixel : 24bit each pixel find FPS : 24 frames/sec

when shooting video, data is generated 1.5Gb/s -> we cannot store this. lack of capacity

Codec​

piece of software that compresses and decompressed the data

  1. CBR (constant bit rate) : suitable for static videos
  2. VBR (variable bit rate) : suitable for dynamic videos.

examples. MPEG1 (CD-ROM) 1.5Mbps MPEG2 (DVD) MPEG 4 (in internet, 64kb)

Streaming videos thru network (Stored video)​

more on chapter 7

challenges : varying bandwidth, packet loss, delay due to conjestion, poor video quality..

How to solve these forms?

Scenario send and resting of transmitting data is performed. (in order not to occupy a bandwidth) -> That's why data is cumulated in form of stairs.

fixed delay

however, fixed delay is not guarenteed. playout bufferin

startup delay. (clident-side buffering, playout delay.) :to cover up the fluctuating network delay(jitter).

challenges, the playout timing must match the original timing. -> needs client-side buffer.

How do you buffer? with startup delay

DASH (Dynamic streaming over HTTP)​

server-side intelligence.

  1. divides video in chunks

  2. encoded chunk at mutiple differnt rates

  3. differnet rate encoding stored in different rates

  4. file is replicated in various CDN nodes

  5. manifest filr provides URL

client-side iintelligence periodically esitmates

OTT. server infrastructure.