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Re: [whatwg] How to expose caption tracks without TextTrackCues

From: Silvia Pfeiffer <silviapfeiffer1@gmail.com>
Date: Tue, 4 Nov 2014 09:20:05 +1100
Message-ID: <CAHp8n2m8JgSCD52zGE-S2DOmTYk1m5xfOGG40m1Q=Za=Tqe2aQ@mail.gmail.com>
To: Brendan Long <self@brendanlong.com>
Cc: WHAT Working Group <whatwg@lists.whatwg.org>
On Tue, Nov 4, 2014 at 3:56 AM, Brendan Long <self@brendanlong.com> wrote:
> On 10/27/2014 08:43 PM, Silvia Pfeiffer wrote:
>> On Tue, Oct 28, 2014 at 2:41 AM, Philip J├Ągenstedt <philipj@opera.com> wrote:
>>> On Sun, Oct 26, 2014 at 8:28 AM, Silvia Pfeiffer
>>> <silviapfeiffer1@gmail.com> wrote:
>>>> On Thu, Oct 23, 2014 at 2:01 AM, Philip J├Ągenstedt <philipj@opera.com> wrote:
>>>>> On Sun, Oct 12, 2014 at 11:45 AM, Silvia Pfeiffer
>>>>> <silviapfeiffer1@gmail.com> wrote:
>>>>>> Using the VideoTrack interface it would list them as a kind="captions"
>>>>>> and would thus also be able to be activated by JavaScript. The
>>>>>> downside would that if you have N video tracks and m caption tracks in
>>>>>> the media file, you'd have to expose NxM videoTracks in the interface.
>>>>> VideoTrackList can have at most one video track selected at a time, so
>>>>> representing this as a VideoTrack would require some additional
>>>>> tweaking to the model.
>>>> The "captions" video track is one that has video and captions rendered
>>>> together, so you only need the one video track active. If you want to
>>>> turn off captions, you merely activate a different video track which
>>>> is one without captions.
>>>> There is no change to the model necessary - in fact, it fits perfectly
>>>> to what the spec is currently describing without any change.
>>> Ah, right! Unless I'm misunderstanding again, your suggestion is to
>>> expose extra video tracks with kind captions or subtitles, requiring
>>> no spec change at all. That sounds good to me.
>> Yes, that was my suggestion for dealing with UA rendered tracks.
> Doesn't this still leave us with the issue: "if you have N video tracks
> and m caption tracks in
> the media file, you'd have to expose NxM videoTracks in the interface"?

Right, that was the original concern. But how realistic is the
situation of n video tracks and m caption tracks with n being larger
than 2 or 3 without a change of the audio track anyway?

> We would also need to consider:
>   * How do you label this combined video and text track?

That's not specific to the approach that we pick and will always need
to be decided. Note that label isn't something that needs to be unique
to a track, so you could just use the same label for all burnt-in
video tracks and identify them to be different only in the language.

>   * What is the track's "id"?

This would need to be unique, but I think it will be easy to come up
with a scheme that works. Something like "video_[n]_[captiontrackid]"
could work.

>   * How do you present this to users in a way that isn't confusing?

No different to presenting caption tracks.

>   * What if the video track's kind isn't "main"? For example, what if we
>     have a sign language track and we also want to display captions?
>     What is the generated track's kind?

How would that work? Are you saying we're not displaying the main
video, but only displaying the sign language track? Is that realistic
and something anybody would actually do?

>   * The "language" attribute could also have conflicts.

How so?

>   * I think it might also be possible to create files where the video
>     track and text track are different lengths, so we'd need to figure
>     out what to do when one of them ends.

The timeline of a video is well defined in the spec - I don't think we
need to do more than what is already defined.

Received on Monday, 3 November 2014 22:20:49 UTC

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