Dynamic Adaptive Streaming over HTTP (DASH) – Standards and Design PrinciplesErmin Hodžić

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Why?

•Currently we have:•Real-time Transport Protocol• End-to-end, real-time, transfer of stream data. Built mostly on UDP.

Sessions. Special port.

•Progressive download• Download and play at the same time. HTTP. CDN networks.

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What else do we need?

•A good idea would be a method that is both:•HTTP-based• CDNs. Firewall-friendly. Widely supported. No sessions.

•Adaptive• Seeking. Bitrate-switching. Bandwidth-efficient. Simple.

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HTTP-based streaming network

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An example of adaptation

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Ladies & Gentlemen: DASH

• Specification allows everything aforementioned•Media presentation•Media presentation description• XML

•DASH client• Place where all the work is being done

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DASH sample workflow

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DASH overview

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Media presentation

• Structured collection of encoded data

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• Each period has a starting time and duration•Consists of representations 10

•Representations are alternative forms of the streamed data• They consists of segments 11

• Segments contain data and metadata•Units that can be directly accessed via

HTTP URL 12

• Initialization segment Metadata describing the content.

•Media segments The actual data with its info.

• Self-Initializing Media Segment Hybrid.13

Segments

•May contain subsegments• Self-contained sets of one or more consecutive movie fragments (F

on pictures)

• Segment index• Subsegments, timing and stream access information (S on pictures)

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Segment Index• Nested Segment Indices

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Summary

• Syntax and semantics of Media Presentation Description• Format of Segments• Flexibility• Size and duration of segments• Number of representations• Frequency and position of random access points• The transport of MPD

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Notes: Live Streaming

• Full MPD unknown•Dynamically update existing MPDs

and send new ones on the fly• Seeking can be omitted to increase

bitrate (unless time-shift is supported)

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