WebVTT beyond captions
Examples and Needs
- Use the timeline search - search for "chicken" - success!
Jeroen: three things I am interested in 1. preview thumbnails - make it a "kind" 2. chapters - can we put more than just text into chapters 3. how to put track inband into live streams
- we're providing urls for images
- or sprite them with media fragment URIs? (YouTube?, Hulu, Brightcove, JWPlayer?)
- base64 encoded images as cue content
- Apple trickplay: provides offsets for iframes
JW: Native implementation in players in browsers?
JW: lots of players are doing this nowadays
PJ: extracting iframes by browser is somewhat not useful
- might get black frames at beginning
- need to buffer all the video
- prefer linking to images
SP: is the proposal to introduce a new @kind="thumbnails" track?
PS: anything that goes into a img @src attribute
SP: do we need to do responsive images?
PJ: possibly - eventually
JN: we can easily extract the images from inband easily because we have offsets
- I would like to introduce an inband version of a @kind="thumbnails" track
JN: let's make sure we introduce a kind="thumbnails" track asap because too many people need/use it
SP: are chapters with thumbnails the same as a thumbnail track?
JW: a thumbnail track will have a higher frequency of images
MD: Should the server just define an API for how to load the images?
JN: you want the images served ahead of time
MD: do ppl use <track> and <video>
JW: smaller companies are starting to really get on the bandwagon
- we need a new @kind="thumbnails" track
- should contain a URL that would be interpreted by an <img> element (or a <div> with the bg set?
- if you want a binary blob, just us a data URI
- if you want to use a sprite, use media fragment URIs? (good first use of spatial media fragment URIs? actually - not implemented yet)
JW: there is interest for more rich chapter content; in particular images
JW: we support this functionality where we have small text markers in the timeline
JW: Playlist with a title, text and image
PJ: could we just use a thumbnail track with a chapter track?
PJ: chapters have images that represent them - thumbnail tracks have images that are at that point in time
JN: if you click on the seek bar at a representative image, ideally you want to display the video from the point in time where the image is taken
PJ: I don't know how we deal with this in the browser in a native way
SP: I think we need a single "thumbnails" track that is always active
- but the example that JW showed includes both a thumbnail and some descriptive text on top of the chapter title text
JW: I'd like to see a thumbnail be part of chapters; descriptive text not so much
Silvia: I think the display that JW has with images, title & descriptive text is a good example for a metadata track - it's displayed outside the video frame anyway
- but if all browsers say that chapters always contain images, then we've obviously underspecified chapter tracks
JN: we always display thumbnails with chapter titles
PJ: if it's a real use case, maybe we should extend the spec
SP: should we include thumbnails into chapters?
PJ: le'ts experiment with thumbnail tracks first
- general agreement that that type of track is more important
Inband tracks for live video
JW: how can we transport text tracks in live video?
- in particular we have cue start times only with no end time - end times are determined by the start of the next cue; mostly for captions
PS: and use blank cues to get breaks
JW: it's a good proposal
PJ: how do we deal with chapters in live streaming?
SP: do they even make sense?
PS: for DVR, yes
JW: workflow - ppl want their content available as fast as possible
PJ: what to do for thumbnails for DVR? What if there is already containers that have in-band thumbnails? We should support that.
PJ: it seems weird to put a condensed version of the movie into the movie
MD: is there an action plan for live VTT?
- NEXT keyword instead of end time would enable support of live captioning
- need to support live VTT - needs a spec change to stop blocking loading until all cues have been loaded
- VC: it seems like cross-domain loading of VTT is blocked in the spec, but no browser implements it
- PJ: same-origin, cross-origin sandboxed, cross-origin DOM-exposed are the three available options
- VC: yes, but nobody has implemented it
- JN: in-band metadata cues are not yet exposed to iOS to the browser
- Sam: 2nd screen use cases; metadata in cues for DOM interaction
- MD: live MPEG-DASH support ? We need data events to JS from text tracks from HLS.
- Steve: Re-using Track / Cue infrastructure for advertising (VMAP).