On Mon, 26 Jul 2010 16:53:43 +0200, Silvia Pfeiffer
<[email protected]> wrote:
On Mon, Jul 26, 2010 at 11:25 PM, Philip Jägenstedt
<[email protected]>wrote:
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>
Does this actually work in Opera now?
Yes, when I have a HelloWorld.webm file available it starts playing. It
also works in Firefox 4b1 and it should work in Chrome and Safari too
unless they are buggy.
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.
Sure, but this is only a snippet of an actual application. If, e.g., you
want to step through a list of videos (maybe an automated playlist) using
script and you need to provide at least two different formats with
<source>,
you'd want to run this algorithm frequently. While this is a good
solution,
authors may still end up doing it in sequence, in which case I guess you
may
indeed need to run resource selection three times: once every time a @src
attribute is changed on a <source> element.
Right, I realize there are actually situations where it isn't a pointless
exercise as in the above. If you're already using scripts, though, you
could actually call canPlayType yourself and use the first one that works:
exts.forEach(function(ext) {
if (video.canPlayType("video/"+ext)) {
video.src = "movie_300."+ext;
return false;
}
});
I expect this will be interoperable right now and it's easier to
understand exactly what's going on.
Looking again at the resource selection algorithm, the second step is to
await a stable state, i.e. wait until the current script has finished.
Given that, it wouldn't be a big problem to let modification of src
attributes on source elements trigger resource selection, you won't get
the 3-2-1 problem I mentioned earlier. However, then I would argue that
modifying type and media should also have the same effect, as those affect
the outcome of resource selection. In the end, my suggestion is still no
spec change, except for editorial changes to clarify.
--
Philip Jägenstedt
Core Developer
Opera Software
