Hi There,
There is no "dynamic media component customization or creation" documentation per se. At least I don't know and could not find anywhere.
Anyhow, if you got access to AEM instance, you can check dynamic media component in AEM at /libs/dam/components/scene7/dynamicmedia.
This component can be customized however having said that, it is a bit more involved. Dynamic media component not only creates the required scene7 publish url correctly depending on the MIME type, it also takes care of showing the right type of presets to you to choose from. It also uses a lot of java scripting because smart crop(for videos particularly)depends on viewer preset which is not a just server side hosted file but also depends on client side javascript to do a lot of manipulation.
So in all, take reference component for closer look and then customize. Also, bump up any estimation for this kind of activity as it is not as simple as it seems with all the complexities involved.
Thanks!