- From: Laura Carlson <laura.lee.carlson@gmail.com>
- Date: Fri, 5 Jan 2018 12:26:08 -0600
- To: John Foliot <john.foliot@deque.com>
- Cc: public-low-vision-a11y-tf <public-low-vision-a11y-tf@w3.org>
Hi John, Added the captioning verbiage per your info. I tweaked it a bit (adding a list) to simply and promote scanability. If you see anything that should be changed please let me know: https://rawgit.com/w3c/wcag21/text-spacing/understanding/21/text-spacing.html Thanks again. Much appreciated. Kindest Regards, Laura On 1/4/18, Laura Carlson <laura.lee.carlson@gmail.com> wrote: > Hi John, > > Thank you very much for the detailed explanation and excellent text for > the understanding document. I'll incorporate it soon as I get a chance. > > Kindest Regards, > Laura > > On Jan 4, 2018 10:58 AM, "John Foliot" <john.foliot@deque.com> wrote: > >> Hi Laura, >> >> I had to go back and figure out what this was about, but after reading >> [2] >> http://rawgit.com/w3c/wcag21/master/understanding/21/text-spacing.html, >> it comes back to me now. Note that my concern/issue is similar to >> @steverep's issue (canvas = images of text). >> >> At issue is that not all captions are provided as stand-alone text files, >> and as such, not all captions will have the technical ability to be >> 'reformatted' because they are, for all intents and purposes, "images of >> text" burned into the "moving pictures" video file (in a similar way that >> text may be part of a JPEG or PNG file). >> >> In effect, there are multiple ways of providing captions. The most common >> are: >> >> 1. The caption file is and remains a stand-alone text file (using a >> timed-text markup language, either TTML or WebVTT), and the caption >> file is >> supplied via the @track element, like this: >> <video poster="myvideo.png" controls> >> <source src="myvideo.mp4" srclang="en" type="video/mp4"> >> <track src="myvideo_en.vtt" kind="captions" srclang="en" >> label="English"> >> </video> >> (This is often referred to as out-of-band captions) >> >> 2. The caption file (again, similar to above, a time-stamped text >> file) is "bundled" inside of the video wrapper (i.e. .mp4 or .mkv) - >> these >> are file formats that are wrappers or containers that traditionally >> include >> the H.264 encoded video stream, the AAC encoded audio stream, and the >> wrapper formats can also include other associated data files such as >> the >> WebVTT file. Here, the user-agent "looks inside" the video wrapper for >> text >> files that correspond to caption files, and when present exposes them >> to >> the end user. See https://www.w3.org/TR/2011/WD-html5-20110113/video. >> html#sourcing-in-band-text-tracks >> >> <https://www.w3.org/TR/2011/WD-html5-20110113/video.html#sourcing-in-band-text-tracks> >> for more specifics, but the key thing to remember is that the captions >> are >> still being supplied via a seperate time-stamped text file, it's just >> that >> the delivery method (in-band) is different: the caption file is >> 'embedded' >> into the video wrapper, and not referenced via the stand-along @track >> attrribute. >> >> 3. A third method of providing captions is done at the post-production >> level, where text is 'burned' directly into the moving image files. >> While >> less common today than in the past, for certain languages and under >> certain >> conditions this remains a valid and viable option (as it meets the >> functional need of providing captions). These types of captions are >> also >> traditionally known as "Open Captions" as they are present and >> persistent to all users, and cannot be disabled or hidden, as the text >> rendered on screen is actually part of each individual frame of the >> video >> asset itself. >> >> It is this third condition that, due to technical limitations, needs to >> be >> exempted from the SC - there is no way for the end user to manipulate the >> on-screen 'text', because it isn't text, it's a special type of image. >> The >> core difference is that there is no "text file" being used to provide the >> captions, so there is nothing that can be further modified by the >> user-agent(s). >> (The following video may help better explain the production process: >> https://www.youtube.com/watch?v=WzADacd7NMo) >> >> To wrap things up, perhaps the following may meet your need? >> >> Examples of text that are typically not affected by style properties >> <https://www.w3.org/TR/WCAG21/#dfn-style-properties> are images of text >> <http://rawgit.com/w3c/wcag21/master/guidelines/index.html#dfn-images-of-text> >> and >> video captions embedded directly into the video frames, and not provided >> as an associated caption file, which are not expected to adapt. >> >> HTH. >> >> JF >> >> >> >> >> >> >> On Thu, Jan 4, 2018 at 6:32 AM, Laura Carlson >> <laura.lee.carlson@gmail.com >> > wrote: >> >>> Hi John, >>> >>> At the November 13, 2017 AGWG teleconference, you mentioned that the >>> Text >>> Spacing Understanding doc should have verbiage to explain what types of >>> captions are not expected to adapt to the SC's metrics [1]. >>> >>> I put a place holder in the document [2] so it wouldn't fall through the >>> cracks. Would it be possible for you please suggest appropriate verbiage >>> to >>> use? >>> >>> We are very fortunate that you have deep expertise in captioning. Thank >>> you very much for your consideration. >>> >>> Kindest Regards, >>> >>> Laura >>> >>> [1] http://rawgit.com/w3c/wcag21/master/guidelines/index.htm >>> l#text-spacing >>> [2] http://rawgit.com/w3c/wcag21/master/understanding/21/tex >>> t-spacing.html >>> >> >> >> >> -- >> John Foliot >> Principal Accessibility Strategist >> Deque Systems Inc. >> john.foliot@deque.com >> >> Advancing the mission of digital accessibility and inclusion >> > -- Laura L. Carlson
Received on Friday, 5 January 2018 18:26:37 UTC