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Re: Multi-bitrate Quicktime SMIL files


From: Andrew Kirkpatrick
Date: Jun 25, 2007 7:10PM

You're going to format the caption file three times? Yikes. Why not
just make the video sit in the center of a video area and when the video
is smaller in dimension there will be some additional border around the
video but the captions will still take up the same amount of space. In
some cases this will result in captions that are wider than the video,
but it won't be that dramatic and I think it will likely be a better
reading experience.

For the video, I'm not sure about QT's bitrate switch support in SMIL,
but you can easily do this with ref movies to control the video.


> -----Original Message-----
> [mailto: <EMAIL REMOVED> ] On Behalf Of
> Terry Thompson
> Sent: Monday, June 25, 2007 8:41 PM
> To: 'WebAIM Discussion List'
> Subject: [WebAIM] Multi-bitrate Quicktime SMIL files
> Hi All,
> Does anyone have a sample SMIL file that serves captioned
> videos to users at different bitrates? Here's what I'm trying
> to accomplish:
> 1. I have three different Quicktime videos, each encoded at
> different bitrates.
> 2. The physical dimensions vary for each of the videos, which
> affects how many words will fit on a line. Therefore, I also
> have three different caption files (qt.txt).
> 3. I'd like to deliver the correct version of both the video
> and caption text, based on user's bandwidth as detected by
> Quicktime (I don't want to burden users with having to select
> the correct version).
> I know that in the SMIL file, <switch> in combination with
> the system-bitrate attribute allows me to present different
> objects for different bitrates, but I'm not clear how best to
> use <switch>. Here's pseudo-code for what I have currently:
> <head>
> <layout>
> <switch>
> <!-- define three <root-layout> elements, one for each
> system-bitrate --> </switch>
> <!-- define all possible regions with id's like
> "video_modem", "video_high", etc.--> </layout> </head> <body> <par>
> <switch>
> <!--choice of <video> elements, one for each system-bitrate.
> Each has a unique region attribute corresponding with
> one of the regions defined above -->
> </switch>
> <switch>
> <!--choice of <textstream> elements, same approach as
> with video.-->
> </switch>
> </par>
> </body>
> This actually works ok for the modem version, but for the
> higher bandwidth versions the Quicktime Player window is the
> same size as the modem version - too small to accommodate the
> larger video. It's as if the <root_layout> element doesn't
> respond to being included within <switch>. I've tried 101
> variations on the above, which usually fixes one problem but
> creates another. I think I just need to study a proven
> template if others have already done this.
> Thanks for any help!
> Terry
> Terry Thompson
> Technology Specialist, DO-IT
> University of Washington