I know this is an old question, and directed at Windows 7 N, but this answer most likely will work on Windows 7 as well. Since I couldn't find the answer anywhere, I played around with Process Monitor (Sysinternals) to find the required files and registry keys. Tested successfully on Pale Moon 28.2.1 (x64) with H264 playback on Twitter and YouTube.
On Windows 10 N 64-bits, all you seem to need is the following (at least for H264 playback):
The file mfperfhelper.dll in your application folder (or Windows\System32 folder)
The file msmpeg2vdec.dll in your Windows\System32 folder
The file mf.dll in your Windows\System32 folder
The file mfplat.dll in your Windows\System32 folder
The file evr.dll in your Windows\System32 folder
Extract these files from the Media Feature Pack installation file appropriate for your Windows version architecture (64-bits - amd64).
The following registry entries: (copy/paste to .reg file and import by double-clicking the file)
Windows Registry Editor Version 5.00
[HKEY_CLASSES_ROOT\CLSID\{62CE7E72-4C71-4D20-B15D-452831A87D9D}]
@="Microsoft H264 Video Decoder MFT"
[HKEY_CLASSES_ROOT\CLSID\{62CE7E72-4C71-4D20-B15D-452831A87D9D}\InprocServer32]
@="C:\\Windows\\System32\\msmpeg2vdec.dll"
"ThreadingModel"="Both"
[HKEY_CLASSES_ROOT\CLSID\{e79167d7-1b85-4d78-b603-798e0e1a4c67}]
@="MF Media Source Activate"
[HKEY_CLASSES_ROOT\CLSID\{e79167d7-1b85-4d78-b603-798e0e1a4c67}\InProcServer32]
@="C:\\Windows\\System32\\mfcore.dll"
"ThreadingModel"="Both"
Why can't you install the Windows Media Feature Pack? – slhck – 2014-09-18T09:15:47.817
1I chose N version to have system without it. I don't want to install it. There has to be some other way to make it work. – user369708 – 2014-09-18T09:36:44.953