bakkenb
commented
6 years ago +1 to this. It is the same concept of developing web sites or web applications. The more you add accessibility considerations in from the beginning, the easier it is to make it accessible. If producers are thinking of accessibility up front, they will prepare to have additional footage captured and available for an audio described version of the media file. This is important to point out as it will save a relatively large amount of time and cost when all said and done.
It may be worth noting that in some cases it is quite simple to produce alternative videos with extended descriptions, rather than pausing the content. For example, in the Perspectives videos we had sufficient filming materials to extend some of the scenes and create pauses for the audio descriptions. The effort for doing this was minimal because the videos were short and we considered this from the start and during the filming. The result was the same user experience for both versions of the video without additional cost. This is obviously not generalizable to the production of all extended descriptions, but should be noted for these who have an opportunity to consider this option from the start of the video production process.