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Re: vodcasting


From: John Foliot
Date: Nov 28, 2006 11:00AM

Andrew Kirkpatrick wrote:
> SMIL isn't really a layer per se, the smil file is interpreted by the
> player and the media presentation is assembled using the items
> referenced by the smil. This works for Real players and is also used
> in QT, but is not the only way to get captions in QT. WMP and Flash
> operate differently.

SMIL is an XML based language that allows for a number of things: it can be
used to create a "reference" file, the container file that references both
the media stream feed as well as the caption text file - it can also be used
to position these elements on screen. SMIL notation also allows for the
"time-stamping" of text transcript so that it can be synched with the media
stream. As such, SMIL is a markup language rather than a technology.

Real and QuickTime currently support the "envisioned" method of SMIL
delivery, where the media and transcript remain separate entities that are
"blended" together in the media player (think similar to Frames). Sadly,
neither player will support the SMIL variant of the other - SMIL files
created for QuickTime will not natively play in the Real player, and

QuickTime (Pro) also allows for the "importing" of the time-stamped XML/SMIL
file, and the creation of a separate, open-captioned .MOV file. Using
third-party extensions, you can also do the same thing to Flash movies:
bring both a video stream and time-stamped SMIL transcript into the
environment and export as a captioned Flash file (.swf). Microsoft uses
SAMI, which is a Redmond-ized variant of SMIL, that only works in Microsoft
based players.

>> My question is: how about when it's being watched on a video
>> iPod or similar device? Provide Open Captions in that case?
> Open captions would work. The ipod can play the following:
> 1) H.264 video, up to 1.5 Mbps, 640 x 480, 30 frames per sec.,
> Baseline Low-Complexity Profile with AAC-LC audio up to 160 kbps, 48
> Khz, stereo audio in .m4v, .mp4, and .mov file formats
> 2) H.264 video, up to 768 kbps, 320 x 240, 30 frames per sec., Baseline
> Profile up to Level 1.3 with AAC-LC audio up to 160 kbps, 48 Khz,
> stereo audio in .m4v, .mp4, and .mov file formats
> 3) MPEG-4 video, up
> to 2.5 Mbps, 640 x 480, 30 frames per sec., Simple Profile with
> AAC-LC audio up to 160 kbps, 48 Khz, stereo audio in .m4v, .mp4, and
> .mov file formats
> I haven't tested if smil is supported in the iPod, but I'm betting
> not. Ask Apple to be sure.

The "envisioned" variant of SMIL is currently not supported in the iPod
(i.e.: separate media and transcript), although open captioned videos can be
created. While some have argued that the captioning may be "too small"
(love him or leave him) Joe Clark debunks that myth fairly succinctly at

Using QuickTime Pro, and SMIL notated transcripts you can create an
Open-captioned .MOV file fairly easily.

> There is also the possibility that there is a tool that can take a
> smil/qt.txt/.mov combination and create a open captioned m4v, but
> I've never heard of one yet.

Ah, another Holy Grail

>> How to differentiate the files - watched on the Web w/SMIL
>> vs. watched on iPod w/Open Captions? I don't have a video
>> iPod or I'd try this
> Another question is whether you serve up the same video file at all
> to these different environments.

Yes, and we need to be careful that we don't link directly to a .SMIL file,
as depending on which player(s) you have installed, the SMIL file *may not*
work as expected, as again Real's SMIL and QT's SMIL are not inter-operable.
Best practice here is to create "native" reference files that then point to
the SMIL file.

While the SMIL markup language allows us to now created synched media files,
the "embedded, open caption" method, while the most predictable in terms of
outcome, has some flaws attached to it, as the text transcript becomes
embedded into the media - think text inside of a JPEG or GIF - same problem.
Conversely, with the transcript remaining outside of the media file proper,
the text can be re-purposed (print transcript separately?) and is also
index-able and searchable - two key considerations as "movies" explode onto
the web.

Finally, while the iPod does not currently support the "envisioned" SMIL of
separate media and transcript files, it is my understanding that Apple is
aware that this is a "problem", although what their plans are to address it
are not known (at least I have not heard).

I recently did a brief, introductory session on SMIL; the S5 presentation
can be found at: http://soap.stanford.edu/presentations/smil/ (Using the
magic of Print Style Sheets, printing the presentation will also provide the
speaking notes, and supplemental links not obvious in the slide show)
Please note that due (in part) to the images used, the S5 presentation has
been optimized for full screen display (F11).


John Foliot
Academic Technology Specialist
Stanford Online Accessibility Program
Stanford University
560 Escondido Mall
Meyer Library 181
Stanford, CA 94305-3093