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Archive for October, 2008

Bay area meetup details

Monday, October 27th, 2008

The bay area meetup will be Tuesday 7PM (October 28) at St Stephen's Green in Mountain View. If you have any further questions feel free to ask them in a comment here or on IRC.

To be perfectly clear, the meeting is open to everyone who wants to come. All that is required is that you actually show up at the pub. See you there!

Posted in WHATWG | No Comments »

This Week in HTML 5 – Episode 10

Monday, October 20th, 2008

Welcome back to "This Week in HTML 5," where I'll try to summarize the major activity in the ongoing standards process in the WHATWG and W3C HTML Working Group.

The big news this week is offline caching. This has been in HTML 5 for a while, but this week Ian Hickson caught up with his email and integrated all outstanding feedback. He summarizes the changes:

  • Made the online whitelist be prefix-based instead of exact match. [r2337]
  • Removed opportunistic caching, leaving only the fallback behavior part. [r2338]
  • Made fallback URLs be prefix-based instead of only path-prefix based (we no longer ignore the query component). [r2343]
  • Made application caches scoped to their browsing context, and allowed iframes to start new scopes. By default the contents of an iframe are part of the appcache of the parent, but if you declare a manifest, you get your own cache. [r2344]
  • Made fallback pages have to be same-origin (security fix). [r2342]
  • Made the whole model treat redirects as errors to be more resilient in the face of captive portals when offline (it's unclear what else would actually be useful and safe behavior anyway). [r2339]
  • Fixed a bunch of race conditions by redefining how application caches are created in the first place. [r2346]
  • Made 404 and 410 responses for application caches blow away the application cache. [r2348]
  • Made checking and downloading events fire on ApplicationCache objects that join an update process midway. [r2353]
  • Made the update algorithm check the manifest at the start and at the end and fail if the manifest changed in any way. [r2350]
  • Made errors on master and dynamic entries in the cache get handled in a non-fatal manner (and made 404 and 410 remove the entry). [r2348]
  • Changed the API from .length and .item() to .items and .hasItem(). [r2352]

And now, a short digression into video formats...

You may think of video files as "AVI files" or "MP4 files". In reality, "AVI" and "MP4" are just container formats. Just like a ZIP file can contain any sort of file within it, video container formats only define how to store things within them, not what kinds of data are stored. (It's a little more complicated than that, because container formats do limit what codecs you can store in them, but never mind.) A video file usually contains multiple tracks -- a video track (without audio), one or more audio tracks (without video), one or more subtitle/caption tracks, and so forth. Tracks are usually inter-related; an audio track contains markers within it to help synchronize the audio with the video, and a subtitle track contains time codes marking when each phrase should be displayed. Individual tracks can have metadata, such as the aspect ratio of a video track, or the language of an audio or subtitle track. Containers can also have metadata, such as the title of the video itself, cover art for the video, episode numbers (for television shows), and so on.

Individual video tracks are encoded with a certain video codec, which is the algorithm by which the video was authored and compressed. Modern video codecs include H.264, DivX, VC-1, but there are many, many others. Audio tracks are also encoded in a specific codec, such as MP3, AAC, or Ogg Vorbis. Common video containers are ASF, MP4, and AVI. Thus, saying that you have sent someone an "MP4 file" is not specific enough for the recipient to determine if they can play it. The recipient needs to know the container format (such as MP4 or AVI), but also the video codec (such as H.264 or Ogg Theora) and the audio codec (such as MP3 or Ogg Vorbis). Furthermore, video codecs (and some audio codecs) are broad standards with multiple profiles, so saying that you have sent someone an "MP4 file with H.264 video and AAC audio" is still not specific enough. An iPhone can play MP4 files with "baseline profile" H.264 video and "low complexity" AAC audio. (These are well-defined technical terms, not laymen's terms.) Desktop Macs can play MP4 files with "main profile" H.264 video and "main profile" AAC audio. Adobe Flash can play MP4 files with "high profile" H.264 video and "HE" AAC audio. Of course, it's a little more complicated than that.


r2332 adds a navigator.canPlayType() method. This is intended for scripts to query whether the client can play a certain type of video. There are two major problems with this: first, MIME types are not specific enough, as they will only describe the video container. Learning that the client "can play" MP4 files is useless without knowing what video codecs it supports inside the container, not to mention what profiles of that video codec it supports. The second problem is that, unless the browser itself ships with support for specific video and audio codecs (as Firefox 3.1 will do with Ogg Theora and Ogg Vorbis), it will need to rely on some multimedia library provided by the underlying operating system. Windows has DirectShow, Mac OS X has QuickTime, but neither of these libraries can actually tell you whether a codec is supported. The best you can do is try to play the video and notice if it fails. [WHATWG thread]

Other interesting changes and discussions this week:

Around the web:

Tune in next week for another exciting episode of "This Week in HTML 5."

Posted in Weekly Review | 5 Comments »

WHATWG meetups

Friday, October 17th, 2008

Next week is the W3C Technical Plenary in Mandelieu, France. Several WHATWG contributors will be hanging out there attending W3C Working Group meetings (CSS, WebApps, HTML) and the Technical Plenary Day. Longtime WHATWG contributor and hacker Henri Sivonen will feature on a panel discussing the future of XML. Silvia Pfeiffer, who has contributed to discussions on video in HTML, will give a lightning talk titled "Beyond HTML5 video". If you happen to be near Mandelieu next week let us know so we can meet up! (E.g., by leaving a comment here, joining our IRC channel or by sending an e-mail to e.g. Ian, Henri, Ben, Lachlan, or Anne (me).)

The week after that several WHATWG contributors are hoping to meet up in a bar in Mountain View, close to San Francisco. Michael Carter (Web Sockets fame) is organizing that through the WHATWG specifications mailing list. It will likely be Tuesday October 28 at 7PM. More details will be announced later. If you want to come please let Michael Carter know. Leaving a comment on this blog entry is probably good enough.

Posted in WHATWG | 3 Comments »

This Week in HTML 5 – Episode 9

Tuesday, October 14th, 2008

Welcome back to "This Week in HTML 5," where I'll try to summarize the major activity in the ongoing standards process in the WHATWG and W3C HTML Working Group.

Most of the changes in the spec this week revolve around the <textarea> element.

Shelley Powers pointed out that I haven't mentioned the issue of distributed extensibility yet. (The clearest description of the issue is Sam Ruby's message from last year, which spawned a long discussion.) The short version: XHTML (served with the proper MIME type, application/xhtml+xml) supports embedding foreign data in arbitrary namespaces, including SVG and MathML. None of these technologies (XHTML, SVG, or MathML) have had much success on the public web. Despite Chris Wilson's assertion that "we cannot definitively say why XHTML has not been successful on the Web," I think it's pretty clear that Internet Explorer's complete lack of support for the application/xhtml+xml MIME type has something to do with it. (Chris is the project lead on Internet Explorer 8.)

Still, it is true that XHTML does support distributed extensibility, and many people believe that the web would be richer if SVG and MathML (and other as-yet-unknown technologies) could be embedded and rendered in HTML pages. The key phrase here is "as-yet-unknown technologies." In that light, the recent SVG-in-HTML proposal (which I mentioned several weeks ago) is beside the point. The point of distributed extensibility is that it does not require approval from a standards body. "Let a thousand flowers bloom" and all that, where by "flowers," I mean "namespaces." This is an unresolved issue.

Other interesting changes this week:

Around the web:

Tune in next week for another exciting episode of "This Week in HTML 5."

Posted in Weekly Review | 2 Comments »

This Week in HTML 5 – Episode 8

Wednesday, October 8th, 2008

Welcome back to "This Week in HTML 5," where I'll try to summarize the major activity in the ongoing standards process in the WHATWG and W3C HTML Working Group.

It's time to catch up on the myriad of changes to the HTML 5 spec. The big news this week is the continued merging of Web Forms 2 into HTML 5.

In other news, Andy Lyttle wants to standardize one particular feature of <input type="search"> (which is already supported by Safari, but not standardized): placeholder text for input fields. The text would initially display in the input field (possibly in a stylized form, smaller font, or lighter color), then disappear when the field receives focus. Lots of sites use Javascript to achieve this effect, but it is surprisingly difficult to get right, in part because no one can quite agree on exactly how it should work. Mozilla Firefox displays the name of your current search engine in its dedicated search box until you focus the search box, at which point it blanks out and allows you to type. Safari's search box is initially blank (at least on Windows), and only displays the name of your default search engine after it has received focus and lost it again. Google Chrome's "omnibox" displays "Type to search", right-justified, even when the omnibox has focus, then removes it after you've typed a single character. Adding an <input placeholder> attribute would allow each browser on each platform to match their users' expectations (and possibly even allow end-user customization) of how placeholder text should work for web forms. Discussion threads: 1, 2, 3. So far, there is no consensus on whether this should be added to HTML 5, or what the markup would look like.

Other interesting changes this week:

Around the web:

Tune in next week for another exciting episode of "This Week in HTML 5."

Posted in Weekly Review | 6 Comments »