Bottom line up front: Re-installing Microsoft Visual C++ Runtime 2012 Update 4 solved this issue for me. It must be this specific version of the runtime.
Details:
Read the steps below carefully as I doubt this solution will work for all variants of this error condition. For example, many people have indicated that Adobe's guidance worked for them.
Like many others across the internet, this problem vexed me. For over a year. I tried Adobe's guidance to no avail. I tried un-/reinstalling Lightroom. No effect. I tried installing Premiere Rush thinking that it would include a module shared with Lightroom. Nope. I tried importing a video into Photoshop. No joy.
...BUT the error message from Photoshop was subtly different. This led me to discover where this DynamicLinkMediaServer component resides (on Windows):
[Program Files]\Adobe\Adobe Lightroom Classic\Helpers\DynamicLinkMediaServer
I attempted to run "dynamiclinkmediaserver.exe" directly and was presented with two new error messages:
"...cannot proceed because MSVCP110.dll was not found" and "...because MSVCR110.dll was not found".
I next looked at the folder [Windows]\system32 (where most core DLLs are installed) and confirmed that neither MSVCP110.dll nor MSVCR110.dll existed (though other variants of these DLLs were there). Those clues led me to determine which specific installer package contains those DLLs.
I installed the Microsoft Visual C++ Runtime 2012 Update 4 and confirmed both DLLs were then installed.
I again tried running "dynamiclinkmediaserver.exe" directly and was pleased to find no error messages displayed.
Next, I attempted to import one of the videos that Lightroom refused to accept earlier - and it WORKED. After over a year of vexation, Lightroom is once again allowing me to include video assets in my catalog.
Good luck!
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