1.
Institut Mines-Télécom
Report of
WebVTT implementation
Cyril Concolato
m30301

2.
Institut Mines-Télécom
Status
 Implementation within GPAC
• http://gpac.sourceforge.net
• 14496-12
• 14496-30
 Support for WebVTT packaging with MP4Box
 Support for WebVTT playback with MP4Client (&
others)
 Plan to support next
• PlainText (SVG, HTML, …)
• TTML (with meta box) – test suite available ?
31/07/2013 GPAC & WebVTT - m303012

3.
Institut Mines-Télécom
Packaging into WebVTTCueBoxes
 Basic usages
MP4Box -add file1.vtt:lang=en subtitle1.mp4
MP4Box -add file2.srt:FMT=VTT:lang=en subtitle2.mp4
• More options (layout, edit list, frame rate change…)
• More usages: split, concatenate, export (SRT -> WebVTT)
• Problem: 3GPP Text Box for WebVTT ?
31/07/2013 GPAC & WebVTT - m303013

4.
Institut Mines-Télécom
DASH and WebVTT and others
 Basic usage
MP4Box -dash 10000 subtitle.mp4:role=subtitle video.mp4
• Other options (fragment duration …)
• Use of redundant samples if necessary
• Example
─ Possibility to mix 3GPP Timed Text and WebVTT
 Problems
• Exposing track layout in MPD for WebVTT is not always useful
• Missing ability to store the role in the MP4 file format
31/07/2013 GPAC & WebVTT - m303014

5.
Institut Mines-Télécom
Example
<Period duration="PT0H10M0.00S">
<AdaptationSet segmentAlignment="true" group="1">
<Role schemeIdUri="urn:mpeg:dash:role:2011" value="subtitle"/>
<Representation id="1" mimeType="video/mp4" codecs="tx3g"
width="1920" height="1080" startWithSAP="1"
bandwidth="391">
<SegmentTemplate timescale="1000" duration="10000"
media="counter-tx3g_dash$Number$.m4s" startNumber="1"
initialization="counter-tx3g_dashinit.mp4"/>
</Representation>
</AdaptationSet>
<AdaptationSet segmentAlignment="true" group="1">
<Role schemeIdUri="urn:mpeg:dash:role:2011" value="subtitle"/>
<Representation id="2" mimeType="video/mp4" codecs="wvtt"
width="1920" height="1080" startWithSAP="1"
bandwidth="606">
<SegmentTemplate timescale="1000" duration="10000"
media="counter-vtt_dash$Number$.m4s" startNumber="1"
initialization="counter-vtt_dashinit.mp4"/>
</Representation>
</AdaptationSet>
</Period>31/07/2013 GPAC & WebVTT - m303015

6.
Institut Mines-Télécom
Playback of WebVTT in MP4
31/07/2013 GPAC & WebVTT - m303016
MP4
Parser
MP4 File
(WebVTT)
WebVTT
Cues
JavaScript
Conversion
(configurable)
SVG Tiny
1.2
elements
Rendering
GPAC Player

7.
Institut Mines-Télécom
Playback of WebVTT in MP4
 Status
• Tested in the following configurations
─ Local file, progressive http download, DASH
─ With or without video
• Rendering Feature support
─ Top-based line positioning, bottom-based line positioning,
explicit positioning
─ Line wrapping
─ Multiline cues
─ Multiple cues simultaneously
─ Basic text styling: italic, bold, underlined
 Problems?
• Metadata (name,value) pair
─ Regions?
─ Need for a new box
• WebVTTCueSourceIdBox
31/07/2013 GPAC & WebVTT - m303017

8.
Institut Mines-Télécom
Demonstration
31/07/2013 GPAC & WebVTT - m303018