I'm updating the new load algorithm for Firefox's <video>
implementation, I've got some feedback on the recent changes to the load
algorithm. I think the changes are sensible. It wasn't immediately
obvious at first, but after thinking through them, I see the logic
behind them.
We now have three things called load. The "load() method", the "load
algorithm", and the "resource-load algorithm". It might be clearer if
they were called the "load() method", the "resource selection
algorithm", and the "resource fetch algorithm".
From the "using source elements" load algorithm sub-step:
/Search loop:/ Run these substeps atomically (so that the DOM cannot
change while they are running):
1.
If the node after pointer is the end of the list, then jump to
the step below labeled /waiting/.
[...]
7. Waiting: Set the error attribute to a new MediaError object whose
code attribute is set to MEDIA_ERR_NONE_SUPPORTED.
8. Set the element's networkState attribute to the NETWORK_NO_SOURCE value
9. Queue a task to fire a progress event called error at the media
element.
10. Set the element's delaying-the-load-event flag to false. This
stops delaying the load event.
11. Wait until the node after pointer is a node other than the end of
the list. (This step might wait forever.)
There's no step 12; I think the intention is that we return to the
Search loop, but it's not documented.
Step 1 of the load algorithm:
1. While the media element has neither a src attribute nor any source
element children, wait. (This steps might wait forever.)
And further down it says:
If a media element
<http://www.whatwg.org/specs/web-apps/current-work/multipage/video.html#media-element>
whose |networkState
<http://www.whatwg.org/specs/web-apps/current-work/multipage/video.html#dom-media-networkstate>|
has the value |NETWORK_EMPTY
<http://www.whatwg.org/specs/web-apps/current-work/multipage/video.html#dom-media-network_empty>|
is inserted into a document
<http://www.whatwg.org/specs/web-apps/current-work/multipage/infrastructure.html#insert-an-element-into-a-document>,
the user agent must asynchronously invoke the media element
<http://www.whatwg.org/specs/web-apps/current-work/multipage/video.html#media-element>'s
load algorithm
<http://www.whatwg.org/specs/web-apps/current-work/multipage/video.html#concept-media-load-algorithm>.
I think that should be "invoke the load() method"? If it's "invoke the
load() method", running load() will cancel any already running instance
of the load algorithm - e.g. any load which is waiting at step 1 of the
load algorithm. As it's written, the load /algorithm /will be invoked,
which will not cancel any waiting loads, and it could in fact it create
another instance of the load algorithm waiting at step 1 of the load
algorithm. So we would create two concurrent instances of the load
algorithm, both waiting at step 1 of the load algorithm by doing the
following:
var v = document.createVideo();
v.load();
document.body.appendElement(v);
Setting v.src or adding a <source> child element to v will awaken two
instances of the load /algorithm.
/Other than that, the media load spec seems sensible.
All the best,
Chris Pearce.
