Presentation about a DASH test source for live video at PyCon Sweden 2015. It is written in Python and runs in the cloud at http://vm2.dashif.org. It recently became open source at Github as dash-live-source-simulator

1. A Reference DASH Live Video
Source
Torbjörn Einarsson, MobiTV
2015-05-13

2.  Worked with video for 20 years
 16 at Ericsson Research
 4 at MobiTV
 Python for 13 years
 prototyping
 testing tools
 video transport, packaging, analysis, synthesis,
streaming servers
About me

3. Intro
 Video is exploding
 over HTTP
 Standard API in HTML-5
1. File download via URI
2. Streaming using MSE
 Media Source Extension
 MSE => segmented video
 Adaptive Bitrate
 Live
 Players in Javascript
 DASH is agreed way forward
 Standard from MPEG
 Can be extended with
encryption/DRM via EME
Encrypted Media Extensions

4.  Dynamic Adaptive Streaming over HTTP
 Standard from MPEG
 Borrows from HLS, Smoothstreaming etc
 Adds more use cases and flexibility
 Starting to get widely used
 Netflix (Chrome, IE11, Safari 8), Google
(Youtube/Chrome), Microsoft
 Two components
 MPD (manifest)
 Media
DASH

5. DASH IOP
 DASH is huge
 Too many options
 DASH-IF for IOP
 Guidelines
 Reference client:
 dash.js on Github
 Test vectors
 VoD
 Live
 Live testing is hard.
 Needs
 live feed
 live encoder
 Has timing issues
 => Live Simulator
 No feed/encoder
 Can do many test cases

6. MPD
 MPD is manifest
 XML description
 Media links
 Variants
 Timing
 VoD – duration
 Live – start, timeshift,
…
 Flexible:
 multiple periods
 multiple
representations

7. Media Segment
 MP4 (iso) files
 Hiearchy of boxes
 [size][type][content]
 Relatively easy to parse
and change
 Need to change number
& timing

8. Approach
 On-the-fly generation
 mod_python
 DASH VoD Source
 Live config (from scan)
 Options in URL
 Align available content
with wall-clock -> live sync
 MPD : VoD -> live
 Number template
 For time t, a certain segment #
is avail.
 Time-limited services
 Periods
 Use ElementTree package
 Segments:
 Infinite series with correct
timing
 Use struct package

9.  24/7 service one period (MPD never changes)
 This can be compared to show system delay depending on segment
duration (see demo)
 Time-shift-buffer-depth and minimum-update-period can be changed
 Time-limited services (with MPD updates)
 Multiple periods
 Ad signaling
 Add cues for client-side ad insertion
 UTCTiming
 Synchronize client clock with server in different ways
Some test cases

10. DEMO

11.  Apache2 server with mod_python
 Only basic usage
 State-less
 Hosted by DASH-IF at vm2.dashif.org
 Source Code
 Transferred copyright to DASH-IF and became Open
Source last week
https://github.com/Dash-Industry-Forum/dash-live-source-simulator
 Players
 Browser (Chrome): dash.js and shaka-player on Github
 Android: ExoPlayer on Github
Environment

12. Python 2 -> 3 conversion
 MP4 parsing a bit tricky,
since mixture of bytes
and strings
 [size][‘styp’][…]
 Integer divisions …
 Took half-a-day to do
conversion, but…
 Cannot run Python3 easily
 mod_python only runs
one Python version
 mod_wsgi only for 2.6
and 2.7 in our Apache 2.2
setup
The code stays Python 2 for now!

13. ?
THANK YOU
teinarsson@mobitv.com