Dynamic Adaptive Streaming over HTTP (DASH) – Standards and Design Principles Ermin Hodžić 1

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. 2

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. 3

HTTP-based streaming network 4

An example of adaptation 5

Ladies & Gentlemen: DASH Specification allows everything aforementioned Media presentation Media presentation description XML DASH client Place where all the work is being done 6

DASH sample workflow 7

DASH overview 8

Media presentation Structured collection of encoded data 9

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) 14

Segment Index Nested Segment Indices 15

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 16

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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) 18

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