WebVTT Metadata
WebVTT Metadata Common To WebM
Objective
The purpose of this document is to describe WebVTT metadata that are useful in the context of WebM.
Background
See WebVTT in WebM for general background notes.
Metadata Format
It has been proposed that file-wide metadata (see [DEV] or [CHANGE]) be stored at the top of the WebVTT file, and formatted as UNIX-style name-value pairs. This has been refined based on discussion on the webm-discuss and public-testtracks mailing lists [WEBMDISCUSS][W3] to look like the following:
WEBVTT
VTTKind: metadata
VTTDataFormat: <metadata format>
VTTDataHint: <metadata type>
1
00:00:15.000 --> 00:00:17.950
first cue
GPS Data (GeoJSON)
A WebVTT file containing GPS coordinates could be used with e.g., Google Maps or Earth, to give location information while playing back a WebM video. Using a payload that is conducive to use in JavaScript will simplify the parsing of the WebVTT file.
The file-wide metadata used in this case would be:
WEBVTT
VTTKind: metadata
VTTDataFormat: GeoJSON
VTTDataHint: GPS data
With the payload of each cue would being the GeoJSON itself [GeoJSON].
00:00.000 --> 00:01.000
{
"type":"Feature",
"id":"OpenLayers.Feature.Vector_314",
"properties":{},
"geometry":{ "type":"Point", "coordinates":[97.03125, 39.7265625] },
"crs":{
"type":"OGC",
"properties":{ "urn":"urn:ogc:def:crs:OGC:1.3:CRS84" }
}
}
Outstanding Issues
The format of WebVTT metadata is still in flux. The format described here could be used, however, within a <track> element allowing the parsing to be done in JavaScript.
References
[CHANGE]
http://www.w3.org/WAI/PF/HTML/wiki/Media_WebVTT_Changes
[DEV]
http://blog.gingertech.net/2011/06/27/recent-developments-around-webvtt/
[WEBMDISCUSS]
https://groups.google.com/a/webmproject.org/d/topic/webm-discuss/N_g0xchnFM8/discussion
[W3]
http://lists.w3.org/Archives/Public/public-texttracks/2012Apr/0011.html
[GEOJSON]