The law states:
"Equivalent alternatives for any multimedia presentation shall be synchronized with the presentation."
Captioning allows your deaf users to understand multimedia content with audio. This guideline requires your text alternatives from Alternate Text to synchronize with the content. There are many tools to help you, especially a free tool called MAGPie. MAGPie allows you to caption windows media files.
Testing for Multimedia Equivalents
For testing techniques and tools, refer to Checkpoint B (multimedia equivalents) in the CSU Cal Poly Section 508 Manual Website Evaluation Guide found in the Tools section of the Accessibility Compliance Guide.