W3C home > Mailing lists > Public > whatwg@whatwg.org > July 2015

Re: [whatwg] preload="metadata" elements don't necessarily fire "canplay"

From: Philip Jägenstedt <philipj@opera.com>
Date: Mon, 6 Jul 2015 15:44:09 +0200
Message-ID: <CAMQvoC=cJfQ29MPOfd+f4_T0zeETSd-kqEjggFfOAuZGsz48Hw@mail.gmail.com>
To: "Robert O'Callahan" <robert@ocallahan.org>
Cc: WHATWG <whatwg@whatwg.org>, Andrew Scherkus <scherkus@chromium.org>
On Mon, Jul 6, 2015 at 2:19 PM, Robert O'Callahan <robert@ocallahan.org>
wrote:

> On Mon, Jul 6, 2015 at 11:17 PM, Philip Jägenstedt <philipj@opera.com>
> wrote:
>
>> On Wed, Jun 10, 2015 at 6:53 AM, Robert O'Callahan <robert@ocallahan.org>
>> wrote:
>> > In Gecko, <video preload="metadata"> doesn't fire "canplay". This is
>> > allowed (encouraged, even) by the spec, since we can efficiently satisfy
>> > preload="metadata" by stopping decoding after one frame, and if we only
>> > decode one frame then readyState will not advance beyond
>> HAVE_CURRENT_DATA.
>> > However, this may be counterintuitive for Web developers. Also, Chrome
>> > fires "canplay" in this situation (although that's probably part of the
>> > "Chrome fires canplay and canplaythrough willy-nilly" bug). Anyone else
>> > have an opinion on this?
>>
>> Are you having site compat problems related to this?
>
>
> There's https://bugzilla.mozilla.org/show_bug.cgi?id=1165203 (the same
> bug as in the other thread), thought that involves load() as well. I don't
> know of any sites where this causes problems in the absence of load(),
> though I wouldn't be surprised if they exist. I think it would be a good
> idea to align browser behaviors or the spec.
>

Yeah, I agree. In Presto I added some explicit limits to readyState based
on preload so that even for data: URLs or fully cached resources, it
wouldn't progress beyond HAVE_CURRENT_DATA. (However, buffered wasn't
censored, so it could look a bit strange if inspected closely.) Is this how
it works in Gecko too, or is it actually the media framework that makes the
guarantee without any clamping on top of it?

My previous attempts to nail down the precise behavior or preload haven't
gone well, as Hixie considers preload as a hint where anything goes. Even
so, specifying the "normal" behavior seems like a good idea.

In the specific case of preload="metadata", what would you like the spec to
say?

Philip
Received on Monday, 6 July 2015 13:44:35 UTC

This archive was generated by hypermail 2.3.1 : Monday, 6 July 2015 13:44:36 UTC