[whatwg] <video>/<audio> feedback

Silvia Pfeiffer silviapfeiffer1 at gmail.com
Fri May 8 21:09:32 PDT 2009

On Sat, May 9, 2009 at 2:25 AM, David Singer <singer at apple.com> wrote:
> At 23:46  +1000 8/05/09, Silvia Pfeiffer wrote:
>> On Fri, May 8, 2009 at 9:43 AM, David Singer <singer at apple.com> wrote:
>>>  At 8:45  +1000 8/05/09, Silvia Pfeiffer wrote:
>>>>  On Fri, May 8, 2009 at 5:04 AM, David Singer <singer at apple.com> wrote:
>>>>>  At 8:39  +0200 5/05/09, KÞi"tof Îelechovski wrote:
>>>>>>  If the author wants to show only a sample of a resource and not the
>>>>>>  full
>>>>>>  resource, I think she does it on purpose.  It is not clear why it is
>>>>>>  vital
>>>>>>  for the viewer to have an _obvious_ way to view the whole resource
>>>>>>  instead;
>>>>>>  if it were the case, the author would provide for this.
>>>>>>  IMHO,
>>>>>>  Chris
>>>>>  It depends critically on what you think the semantics of the fragment
>>>>>  are.
>>>>>  In HTML (the best analogy I can think of), the web page is not trimmed
>>>>>  or
>>>>>  edited in any way -- you are merely directed to one section of it.
>>>>  There are critical differences between HTML and video, such that this
>>>>  analogy has never worked well.
>>>  could you elaborate?
>> At the risk of repeating myself ...
>> HTML is text and therefore whether you download a snippet only or the
>> full page and then do an offset does not make much of a difference.
>> Even for a long page.
> you might try loading, say, the one-page version of the HTML5 spec. from the
> WhatWG site...it takes quite a while.  Happily Ian also provides a
> multi-page, but this is not always the case.

That just confirms the problem and it's obviously worse with video. :-)

> The reason I want clarity is that this has ramifications.  For example, if a
> UA is asked to play a video with a fragment indication #time="10s-20s", and
> then a script seeks to 5s, does the user see the video at the 5s point of
> the total resource, or 15s?  I think it has to be 5s.

I agree, it has to be 5s. The discussion was about what timeline is
displayed and what can the user easily access through seeking through
the displayed timeline. A script can access any time of course. But a
user is restricted by what the user interface offers.

>> So, the difference is that in HTML the user agent will always have the
>> context available within its download buffer, while for video this may
>> not be the case.
> I'm sorry, I am lost.  We could quite easily extend HTTP to allow for
> anchor-based retrieval of HTML (i.e. convert a 'please start at anchor X'
> into a pair of byte-range responses, for the global material, and then the
> document from that anchor onwards).

Yes, but that's not the way it currently works and it is not a
proposal currently under discussion.

>> This admittedly technical difference also has an influence on the user
>> interface.
>> If you have all the context available in the user agent, it is easy to
>> just grab a scroll-bar and jump around in the full content manually to
>> look for things. This is not possible in the video case without many
>> further download actions, which will each incur a network delay. This
>> difference opens the door to enable user agents with a choice in
>> display to either provide the full context, or just the fragment
>> focus.
> But we can optimize for the fragment without disallowing the seeking.

What do you mean by "optimize for the fragment"? Of course none of the
discussion will inherently disallow seeking - scripts will always be
able to do the seeking. But the user may not find it easy to do
seeking to a section that is not accessible through the displayed
timeline, which can be both a good and a bad thing.


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