On Mon, 26 Jul 2010 15:02:34 +0200, Silvia Pfeiffer
<[email protected]> wrote:
On Mon, Jul 26, 2010 at 7:49 PM, Philip Jägenstedt
<[email protected]>wrote:
On Mon, 26 Jul 2010 02:58:07 +0200, Silvia Pfeiffer <
[email protected]> wrote:
On Sun, Jul 25, 2010 at 3:31 PM, Maciej Stachowiak <[email protected]>
wrote:
On Jul 23, 2010, at 7:16 AM, Philip Jägenstedt wrote:
Silvia made we aware of discrepancy in how browsers implement the
resource
selection algorithm, see forwarded message. It's my assessment that
Opera
is
the only browser following the spec. I've filed this bug with Mozilla:
https://bugzilla.mozilla.org/show_bug.cgi?id=581355
I've also reported bugs in Chrome and Safari, but can't see where they
ended up.
The reason I'm writing this email is that apparently everyone but
myself
has a different interpretation of the spec, so perhaps this is
something
we
need to discuss. Does any other browser ever set the state
NETWORK_NO_SOURCE
at all? I speculated that perhaps other browsers aren't very strict
about
which parts of the algorithm are run synchronously and not, but even
checking the networkState after a setTimeout it still isn't
NETWORK_NO_SOURCE.
Test case:
http://people.opera.com/philipj/2010/07/23/networkState.html
Please fix implementation or spec :)
1) Which behavior is more useful?
2) Sylvia's original issue was with play() - should we ensure that any
time
you call play(), it will cause the media resource to start playing
once
loaded? That seems like the real spec bug.
The problem there with play in Opera was that the @src was changed, but
Opera doesn't run the resource selection algorithm to load it for
play(),
but instead expects to run load() first. The description of play()
however
clearly states as a first step:
1. If the media
element<
http://www.whatwg.org/specs/web-apps/current-work/complete/video.html#media-element
>'s
networkState<
http://www.whatwg.org/specs/web-apps/current-work/complete/video.html#dom-media-networkstate
>attribute
has the value
NETWORK_EMPTY<
http://www.whatwg.org/specs/web-apps/current-work/complete/video.html#dom-media-network_empty
>,
invoke the media
element<
http://www.whatwg.org/specs/web-apps/current-work/complete/video.html#media-element
>'s
resource selection
algorithm<
http://www.whatwg.org/specs/web-apps/current-work/complete/video.html#concept-media-load-algorithm
>
.
This is why we are discussing whether the networkState needs to be
NETWORK_EMPTY or NETWORK_NO_SOURCE after initialisation of a media
element.
Incidentally, that has effects on other elements, too, such as for
<source>
it is stated:
If a source<
http://www.whatwg.org/specs/web-apps/current-work/complete/video.html#the-source-element
>element
is inserted as a child of a media
element<
http://www.whatwg.org/specs/web-apps/current-work/complete/video.html#media-element
>that
has no
src<
http://www.whatwg.org/specs/web-apps/current-work/complete/video.html#attr-media-src
>attribute
and whose
networkState<
http://www.whatwg.org/specs/web-apps/current-work/complete/video.html#dom-media-networkstate
>has
the value
NETWORK_EMPTY<
http://www.whatwg.org/specs/web-apps/current-work/complete/video.html#dom-media-network_empty
>,
the user agent must invoke the media
element<
http://www.whatwg.org/specs/web-apps/current-work/complete/video.html#media-element
>'s
resource selection
algorithm<
http://www.whatwg.org/specs/web-apps/current-work/complete/video.html#concept-media-load-algorithm
>
.
And for @src it is said:
If a src<
http://www.whatwg.org/specs/web-apps/current-work/complete/video.html#attr-media-src
>attribute
of a media
element<
http://www.whatwg.org/specs/web-apps/current-work/complete/video.html#media-element
>is
set or changed, the user agent must invoke the media
element<
http://www.whatwg.org/specs/web-apps/current-work/complete/video.html#media-element
>'s
media element load
algorithm<
http://www.whatwg.org/specs/web-apps/current-work/complete/video.html#media-element-load-algorithm
>.
(*Removing* the
src<
http://www.whatwg.org/specs/web-apps/current-work/complete/video.html#attr-media-src
>attribute
does not do this, even if there are
source<
http://www.whatwg.org/specs/web-apps/current-work/complete/video.html#the-source-element
>elements
present.)
That is kinda strange, too, because really when @src is changed,
resource
selection has to be run first rather than media element load.
The load algorithm is just a wrapper for the resource selection
algorithm
that makes sure that a previously running resource selection algorithm
is
aborted in an orderly fashion and that the state is reset. What's
strange?
I misread that, too. I thought it was pointing to the resource fetch
algorithm and not the media element load algorithm. You're right - this
part
is fine.
Incidentally, your test isn't complete. In my test file, I was actually
setting the @src values of the <source> elements to resources that
existed
and then called the play() function. That activity should, IMO, work. All
browser accept it, except for Opera, which never leaves step 21 because
play() doesn't accept NETWORK_NO_SOURCE for re-running the resource
selection algorithm. That was really my original problem.
I agree that it'd be good if this worked, all else equal. Unfortunately,
making it work would require adding hooks for when the src attribute of
source elements are changed. Since you want to change all of the src
attributes before resource selection runs, you'd either have to delay its
invocation (a.k.a. await a stable state) or have a situation where the
first source is potentially processed 3 times, the second 2 times and the
last 1 time.
My solution:
<video controls width="400px">
</video>
<script type="text/javascript">
var video = document.querySelector("video");
var exts = ["mp4", "webm", "ogv"];
exts.forEach(function(ext) {
var source = document.createElement("source");
source.src = "HelloWorld."+ext;
source.type = "video/"+ext;
video.appendChild(source);
});
video.play();
</script>
Of course, there must be some good reason to use scripts to begin with, as
the result of this is always the same, so you might just as well use
static markup.
--
Philip Jägenstedt
Core Developer
Opera Software
