[Athen] captions for ios devices

N Dogbo ndogbo at gmail.com
Sun Dec 30 21:08:59 PST 2012

Hi Terrill,
Thanks for sharing the good news! This audio description implementation is
really cool. I am also trying to find a video where I can see the text
description with ARIA role alert implementation. So if you can point one out
to me in your video library I'd appreciate that!
I am joining your blog soon!


----- Think not with your EYES and you shall have a perfect VISION! ---

-----Original Message-----
From: athen-list-bounces at mailman1.u.washington.edu
[mailto:athen-list-bounces at mailman1.u.washington.edu] On Behalf Of Terrill
Sent: Friday, December 28, 2012 1:01 PM
To: Access Technology Higher Education Network
Subject: Re: [Athen] captions for ios devices

Hi All,

I'm a little late joining this conversation, but just wanted to share what
we're doing at DO-IT:

We've created a custom media player that uses HTML5 as its primary player,
and JW Player as fallback for those who are using older browsers that don't
support HTML5. We've created a highly accessible custom player that
communicates with both the HTML5 media and JW Player API's so all users -
even those with older browsers - get exactly the same experience and
identical feature sets.

For video files, we're using MP4, which is now supported by most browsers
and will eventually be supported by Firefox (the last major holdout). Until
then, we're also delivering all our videos using Ogg (older videos) or WebM
(newer videos), since those are the formats preferred by Firefox (and Opera,
which only recently began supporting MP4). JW Player also supports MP4, so
that same file works in the fallback player.

For captions, we start with an SRT caption file. The standard format for
HTML5 captions is WebVTT, which at its core is very similar to SRT, so it's
easy to convert the SRT file to WebVTT with just a couple of edits in a text
editor (there are also free tools available that will do the conversion).
Browsers are starting to build in support for WebVTT captions in HTML5, but
from my experience their implementation is still a little buggy, so we
decided to build caption support into our custom controller rather than rely
on browsers to do it.

We upload all our videos to YouTube in addition to showing them on our own
site. For YouTube, we upload the original SRT caption file. And for iOS, we
embed the SRT caption file into our MP4 video file using Handbrake. It's
great that iOS supports that because we're already delivering an MP4 file,
so we don't really have to do anything extra-special - we just use that same
MP4 file for all purposes, including delivery of captions in iOS. I recently
discovered that my iPhone reports that it "Can't play the caption file" on
at least one of our videos, so the iOS caption parser is apparently a little
fussy, but most of the time it seems to work. iOS also supports multiple SRT
files within a single MP4, so that's an effective strategy for delivering
foreign-language subtitles. We aren't supporting subtitles yet on our
videos, but we do have a few of them translated so we're working on
implementing subtitles soon.

Since you mentioned audio description Ken, we're implementing that in a
couple of different ways:

First, we outsource audio description for all our videos. The deliverable
from vendors is a new video, with description mixed into the program audio.
They do a great job of placing description in the best places so it's
minimally intrusive plus they adjust volumes so the description can easily
be heard over background sounds. The media player we've created includes a
Description button that if clicked, swaps the source media file so if the
user is viewing the non-described version the described version is loaded,
and vice versa.

We also provide a text version of the description in a WebVTT file, the same
file format that's used for captions. This form of description is supported
by the HTML5 spec. No browsers support it natively yet, but we built support
into our custom player. The description text is displayed at the appropriate
times just like captions are, but they're displayed in a box that's marked
with ARIA role="alert", which causes screen readers to read the description
as soon as it appears. This is off by default on our player since users have
the option of viewing a professionally described video, but there's a
Preferences button that allows users to experiment with different ways of
getting their description delivered.

One advantage of having a WebVTT-based description, at least as a supplement
to the professionally described alternative version, is that the WebVTT
description file can be used in conjunction with the caption file to build a
transcript. In our transcript we markup the caption and description in such
a way that they're visually distinct, plus we've added the text
"Description:" to the start of each block of description content, hidden to
everyone except screen reader users.

We're planning to make our custom media player available as an open source
project sometime in early 2013. The best place to stay abreast of that is my
blog: http://terrillthompson.com/blog


Terrill Thompson
Technology Accessibility Specialist
DO-IT, Accessible Technology
UW Information Technology
University of Washington
tft at uw.edu

On Thu, Dec 20, 2012 at 2:39 PM, Ken Petri <petri.1 at osu.edu> wrote:

> Hi Dean,


> The Handbrake method works just fine. But if you have a Mac iSubtitle


> you more options.


> Here's the too-long URL on how to do this with Handbrake:




> A short URL to the entire DIY Captioning Techniques page is:

> http://go.osu.edu/diy-captioning


> Other good info in this page as well. The info about how to add an audio

> description track is forth-coming. That technique does, however, require

> QuickTime Pro....



> ken

> --

> Ken Petri

> Program Director, OSU Web Accessibility Center

> 102D Pomerene Hall, 1760 Neil Avenue, Columbus, Ohio 43210

> Office: 614.292.1760 | Mobile: 614.218.1499 | Fax: 614.292.4190

> http://wac.osu.edu | petri.1 at osu.edu




> On Thu, Dec 20, 2012 at 5:10 PM, Sean J Keegan <skeegan at stanford.edu>



>> > I want to learn how to add captions for iOS devices. I found a

>> > vendor site that gives instructions, but it says it only works using

>> > QuickTime Pro on a Mac. I have been unsuccessful in searches to

>> > confirm this. Can someone please tell me whether this is accurate?


>> Hi Dean,


>> Generally speaking, there are two ways to add captions to iOS media:

>> embedding a caption file so that it requires the closed caption decoder;


>> embedding a caption file as a subtitle track.


>> The first method is what I call the "closed caption decoder" solution.

>> This requires that you create an SCC file and embed this file into the

>> original media file. In order to view these captions on an iOS device


>> have to enable the closed caption decoder feature in the Videos menu

>> (Settings > Videos > Closed Captioning). The SCC file is the same file


>> as is used for captioning VHS media content and is a bit of a pain. From

>> what I have found, you need to have Compressor (Mac only) in order to

>> integrate the SCC caption into the original media file.


>> The second method is what I call the "subtitle track" solution. This

>> involves using the subtitle track to embed caption information into the

>> media file. I have had much greater success using this solution as it is

>> far easier to deal with the SRT caption file and the application used to

>> embed the captions (as subtitles) into the original media. I have used


>> application iSubtitle (Mac only) to perform this process. Subler, also


>> only, also works.


>> For Windows, the options are varied. Wondershare Video Converter




>> is one tool that you could try. Previous versions seemed to work with

>> getting a subtitle track into an MP4 media file, so that may be one


>> (I only tried this tool years ago, so your mileage may vary).


>> Handbrake may be an option now that there is improved subtitle support


>> MP4 media files. With a user created SRT caption file, you can run the

>> media file and caption file together through Handbrake to get soft or


>> subtitles (soft-subtitles can be enabled/disabled whereas hard-subtitles


>> burned into the video itself). See


>> for more information. I have not tried this method myself (yet!).


>> Take care,

>> Sean


>> --

>> Sean Keegan

>> Associate Director, Assistive Technology

>> Office of Accessible Education - Stanford University

>> http://studentaffairs.stanford.edu/oae

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