Mm sys 2013-demo
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This document discusses a proof-of-concept for live streaming of video and subtitles within a browser. It uses HTTP Live Streaming to segment video into MP4 files and subtitles into WebVTT text files. A JavaScript player fetches and synchronizes the segments, displaying video using HTML5 video and subtitles via HTML track elements. While functional, the demo has limitations around rendering performance with dense subtitles, lack of seeking support, and HTML5 constraints on cue loading.
![Usage of MP4Box
■ Fragmenting a file repeatedly using -dash-ctx option
MP4Box.exe -dash-live 2000 -rap
-dash-ctx dash-live.txt
-segment-name counter-live
counter.mp4
■ Example of MP4Box’s DASH context
[DASH]
InitializationSegment=counter_liveinit.mp4
BitstreamSwitching=yes
InitializationSegmentSize=860
MaxSegmentDuration=1.000000
NextSegmentIndex=11
NextFragmentIndex=11
PeriodDuration=9.960000
[TrackID_1]
NextDecodingTime=249000
6
Live HTTP Streaming of Video and Subtitles within a Browser
- MMSys Demo 2013](https://image.slidesharecdn.com/mmsys-2013-demo-141219085927-conversion-gate02/85/Mm-sys-2013-demo-6-320.jpg)
Mm sys 2013-demo
- 1. Live HTTP Streaming of Video and Subtitles within a Browser Cyril Concolato Jean Le Feuvre {concolato, lefeuvre} @ telecom-paristech.fr MMSys 2013
- 2. Context 1 ■ Video Streaming is popular on the Web • With subtitle support in VOD • With live streaming solutions (DASH, HLS, …) ■ What about live subtitles ? • Several specifications being developed − ISOBMFF Amendment on Timed Text and Timed Overlays, for use with DASH − WebVTT draft (used in HLS v10) • No deployment yet within browsers ■ Can we today stream and play live video+subtitles within a browser? • Yes ! • Development of a Proof-of-Concept Live HTTP Streaming of Video and Subtitles within a Browser - MMSys Demo 2013
- 3. Architecture 3 Live HTTP Streaming of Video and Subtitles within a Browser - MMSys Demo 2013
- 4. Demonstration Media Formats ■ The ISO Base Media File Format • To carry video stream segments • Conformant to MPEG DASH and Google Chrome restrictions ■ The WebVTT format • To carry subtitle data − as separate text files (not multiplexed in the video container) − Similar to HLS v10, with some differences (no embedded video timing) • Generation of non-overlapping, constant duration segments (compatible with MPEG DASH) ■ MPEG DASH MPD • To represent a dynamic live/long-running streaming service • To enable synchronization of the video and subtitle streams. 4 Live HTTP Streaming of Video and Subtitles within a Browser - MMSys Demo 2013
- 5. Demonstration software components ■ GPAC MP4Box • To produce video segments on-the-fly and delete old ones − From a pre-recorded file (looped indefinitely) ■ VTTLiveGenerator • Ad-hoc tool • To produce subtitle segments on-the-fly, synchronized with the video and delete old ones ■ Google Chrome • Canary version • To display the content using HTML5 and JavaScript 5 Live HTTP Streaming of Video and Subtitles within a Browser - MMSys Demo 2013
- 6. Usage of MP4Box ■ Fragmenting a file repeatedly using -dash-ctx option MP4Box.exe -dash-live 2000 -rap -dash-ctx dash-live.txt -segment-name counter-live counter.mp4 ■ Example of MP4Box’s DASH context [DASH] InitializationSegment=counter_liveinit.mp4 BitstreamSwitching=yes InitializationSegmentSize=860 MaxSegmentDuration=1.000000 NextSegmentIndex=11 NextFragmentIndex=11 PeriodDuration=9.960000 [TrackID_1] NextDecodingTime=249000 6 Live HTTP Streaming of Video and Subtitles within a Browser - MMSys Demo 2013
- 7. Example of Video Content 7 Live HTTP Streaming of Video and Subtitles within a Browser - MMSys Demo 2013
- 8. Example of WebVTT Segment ■ Each segment is a complete WebVTT file with multiple cues, • changing header, cue indices, and timing values WEBVTT Segment 6 61 00:00:12.200 --> 00:00:12.400 This is cue 61 (start: 00:00:12.200 -- end: 00:00:12.400) ... 70 00:00:14.000 --> 00:00:14.200 This is cue 70 (start: 00:00:14.000 -- end: 00:00:14.200) 8 Live HTTP Streaming of Video and Subtitles within a Browser - MMSys Demo 2013
- 9. Example of DASH Description ■ Use of a “dynamic” MPD • No minUpdate attribute • Without updates (assuming known/static timing) ■ A single period with 2 adaptation sets • 1 video representation • 1 subtitle representation • Same video and subtitle segments duration (easy) ■ live-vtt-mp4.mpd 9 Live HTTP Streaming of Video and Subtitles within a Browser - MMSys Demo 2013
- 10. Rendering using Google Chrome Canary ■ HTML page • Use of HTML5 <video> element with an HTML <track> element for playback synchronization • Use of JavaScript code to control the download logic ■ JavaScript algorithm • Fetch and parse the MPD, • Create the <video> and <track> elements, • Determine and fetch the video and subtitles segments using the XMLHttpRequest API, • Feed the video segments to the media decoder engine using the Media Source extension API, • Load each subtitle segment using an HTML5 work- around 10 Live HTTP Streaming of Video and Subtitles within a Browser - MMSys Demo 2013
- 11. Demo 11 Live HTTP Streaming of Video and Subtitles within a Browser - MMSys Demo 2013
- 12. Discussion/Limitations ■ Working demo • Supports time shifting or not • Needs better integration of video & subtitle MPDs at server side • Needs at client side: − Better MPD parsing − Better simple segment index algorithm ■ Issues • Rendering performance problem if more than 4 cues per second • User Interface problem − Unusable built-in UI for long-running live events − Needs custom UI to disable seeking before the first received data • HTML 5 limitations to load cues − No MSE equivalent for cues (outside of VTT in MP4) − No easy method to parse cues 12 Live HTTP Streaming of Video and Subtitles within a Browser - MMSys Demo 2013
- 13. Questions ? Come and see me