2. What happens if the new igdumdim32.dll is used for installation?
3. Did you try using the w7 4680 package with only the igdlh64.inf modded?
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2 and 3. It crashes all video including 3rd party programs. You need the igdumdim64.dll from a newer version and the 32.dll from old version to have audio with windows media player and video with VLC, GOM etc. Even 4K videos play smoothly with GOM player that I tried.
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My device manager is clear, however, as I wrote I don't get full support. The issue is related to these two dll files, so system libraries.