[whatwg] How to handle multitrack media resources in HTML
eric.carlson at apple.com
Tue Apr 12 07:33:52 PDT 2011
On Apr 11, 2011, at 5:26 PM, Ian Hickson wrote:
> On Mon, 11 Apr 2011, Jeroen Wijering wrote:
>> On Apr 8, 2011, at 8:54 AM, Ian Hickson wrote:
>>> There's a big difference between text tracks, audio tracks, and video
>>> tracks. While it makes sense, for instance, to have text tracks
>>> enabled but not showing, it makes no sense to do that with audio
>> Audio and video tracks require more data, hence it's less preferred to
>> allow them being enabled but not showing. If data wasn't an issue, it
>> would be great if this were possible; it'd allow instant switching
>> between multiple audio dubs, or camera angles.
> I think we mean different things by "active" here.
> The "hidden" state for a text track is one where the UA isn't rendering
> the track but the UA is still firing all the events and so forth. I don't
> understand what the parallel would be for a video or audio track.
> Text tracks are discontinuous units of potentially overlapping textual
> data with position information and other metadata that can be styled with
> CSS and can be mutated from script.
> Audio and video tracks are continuous streams of immutable media data.
Video and audio tracks do not necessarily produce continuous output - it is perfectly legal to have "gaps" in either, eg. segments that do not render. Both audio and video tracks can have metadata that affect their rendering: an audio track has a volume metadata that attenuates its contribution to the overall mix-down, and a video track has matrix that controls its rendering. The only thing preventing us from styling a video track with CSS is the lack of definition.
> I don't really see what they have in common other than us using the word
> "track" to refer to both of them, and that's mostly just an artefact of
> the language.
"Track" is more than an artifact of the language, it is the commonly used term in the digital media industry for an independent stream of media samples in a container file.
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