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?
spatial : use redundancy within an image
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
popular Compressing technique
CBR (constant bit rate) : suitable for static videos
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.
divides video in chunks
encoded chunk at mutiple differnt rates
differnet rate encoding stored in different rates
file is replicated in various CDN nodes
manifest filr provides URL
client-side iintelligence periodically esitmates
OTT. server infrastructure.
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