This may be marketing heresy today, but I much prefer to read an online article or transcript than to watch a video or listen to a podcast. In part it is because as a writer, I certainly have a bias for the written word.
But the primary reason I like text: It allows me to save time by skimming the content for information of interest. Contrast this with waiting for a media file to download, the player to open, then having to view or listen to all or most of the file before I can determine if it contains anything relevant.
Although it is easy and inexpensive to create an audio transcript, that may not be your best choice for a written document to accompany the media file. Remember that a verbatim transcript will include every stumble, hesitation, and run-on by the speaker; all the informal language, jargon, and side remarks. When heard, these items are easy to ignore, but when read, they don't always reflect well on the presenter or your company.
With just a little extra effort, you can create a more effective document to offer as a companion to media files for site visitors who prefer reading. A Web article, short white paper, a blog post, or a slide deck can present the same information as the media file, often in a more succinct and polished form.
And by giving your visitors content choices, you will likely find that both text and audio/video forms are well received.
Which documents have you found effective for promoting with online videos, podcasts, Webinars, and similar multimedia files?