Tools & Guidelines
MAGpie2 Additional Audio Description Topics

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Using a Single Audio Description File

Audio descriptions are easy to create, add to media, and conceptualize when each audio description is a single audio file and the start and end of the description coincide with the start and end of the audio file. Descriptions can come from longer audio files, however. Sometimes several audio descriptions are sequenced one after another in a single file, and other times a single audio description comes from a file with a little bit of "excess" audio information that you can't (or don't want to) remove.

To illustrate this, examine the following example: a video has 3 audio descriptions, each 5 seconds long, and playing at 20, 40, and 60 seconds into the video presentation respectively. The first table below demonstrates how these descriptions would be included with each description as its own audio file and the second table demonstrates inclusion of the descriptions as a single file and the different requirements within the MAGpie audio description authoring environment.

Including Audio Descriptions as Separate Files

Row	Media Start	Media End	Audio Resource	Audio Start	Audio End	Audio Transcription
1	:20		ad1.wav			transcription #1
2	:40		ad2.wav			transcription #2
3	1:00		ad3.wav			transcription #3

The SMIL code that is generated is as follows:


<audio begin="0:00:20.00" src="ad1.wav" />
<audio begin="0:00:40.00" src="ad2.wav" />
<audio begin="0:01:00.00" src="ad3.wav" />

Including Audio Descriptions as a Single File

Row	Media Start	Media End	Audio Resource	Audio Start	Audio End	Audio Transcription
1	:20		all_ad.wav	0	5	transcription #1
2	:40		all_ad.wav	7	12	transcription #2
3	1:00		all_ad.wav	14	19	transcription #3

The SMIL code that is generated is as follows:


<audio begin="0:00:20.00" src="all_ad.wav" clip-begin="0:00:00.00" clip-end="0:00:05.00" />
<audio begin="0:00:40.00" src="all_ad.wav" clip-begin="0:00:07.00" clip-end="0:00:12.00" />
<audio begin="0:01:00.00" src="all_ad.wav" clip-begin="0:00:14.00" clip-end="0:00:19.00" />

If the Media End cell was used instead of the Audio End cell, the results would be the same but the SMIL code would differ slightly:


<audio begin="0:00:20.00" end="0:00:25.00" clip-begin="0:00:00.00" src="all_ad.wav" />
<audio begin="0:00:40.00" end="0:00:45.00" clip-begin="0:00:07.00" src="all_ad.wav" />
<audio begin="0:01:00.00" end="0:01:05.00" clip-begin="0:00:14.00" src="all_ad.wav" />

QuickTime Audio Description Playback Issue

QuickTime supports the clip-begin attribute, but only if the timecode is referenced in the SMIL file using the 'npt=' prefix. As a result, when using a single file for audio descriptions in QuickTime, it may be necessary to modify the SMIL for each description, as shown below:


<audio begin="0:00:20.00" end="0:00:25.00" clip-begin="npt=0:00:00.00" src="all_ad.wav" />

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© 2007 Carl and Ruth Shapiro Family National Center for Accessible Media. All rights reserved.