- From: Hugh Guiney <hugh.guiney@gmail.com>
- Date: Thu, 5 Jan 2012 23:13:28 -0500
- To: "Tab Atkins Jr." <jackalmage@gmail.com>
- Cc: Matthew Wilcox <elvendil@gmail.com>, www-style@w3.org
Yep, exactly. On Thu, Jan 5, 2012 at 6:45 PM, Tab Atkins Jr. <jackalmage@gmail.com> wrote: > On Thu, Jan 5, 2012 at 2:20 PM, Hugh Guiney <hugh.guiney@gmail.com> wrote: >> Hope this isn't too divergent; spin-off the thread if necessary, but I >> just read your proposed spec Tab (http://www.xanthir.com/blog/b4810), >> and have some comments. >> >>> You can use it to, for example, require that an HTML <video> element is as wide as its parent element at all times, but maintain a 4:3 ratio. >> >>> However, several common ratios are usually expressed as fractions or explicit ratios, such as "16 by 9". These can be easily expressed using the calc() function, like aspect-ratio: calc(16/9);. >> >> The problem with these is that in the video world, aspect ratio is a >> lot more complicated. When somebody says "4:3" or "16:9", all you can >> really be sure of what they mean is "frame size that is nearly as tall >> as it is wide" and "frame size that is noticeably wider than it is >> tall", respectively. The aspect ratios of video described in these >> terms, more often than not aren't literally 4:3 or 16:9, due to >> varying pixel aspect ratio dimensions. >> >> I explained this problem in some detail on WHATWG a few years back >> (first reply block): >> http://lists.whatwg.org/htdig.cgi/whatwg-whatwg.org/2009-December/024541.html >> >> The problem is, if an author has a 720x480 pixel video, and specifies: >> >> max-height: 480px; >> aspect-ratio: calc(16/9); >> >> What do they get? The blind mathematics are simple, but the correct >> square-pixel width could be 853, 854, 856, 864, 873, or 875 depending >> on the video specification being observed. And that's just on the >> "NTSC" side; there are still other definitions for PAL-area video. >> Most authors and even video professionals are oblivious to these >> conflicting definitions so even if there were a way to specify the >> standard manually it wouldn't be used. >> >> Thus I think the best solution would be a rewording of the spec that >> states the value of aspect-ratio is interpreted literally; that >> depending on the video standard, the shorthands 4:3 or 16:9 may not >> produce the correct ratio. > > So you'd just like a further note to that note, saying that videos are > often not exactly 4:3 or 16:9 due to oddities in encoding standards, > so beware when setting up ratios on dom elements depending on a video > being the same size? > > ~TJ
Received on Friday, 6 January 2012 07:08:24 UTC