Identify the actual launch route
Open the intended permitted file from within mpv.net, then compare double-clicking that same file in File Explorer. Record which application opens in each case. Do not compare different file types, since each extension can have its own default application choice.
A hypothetical result is that an MP4 opens in one player while an MKV opens in another. That does not mean the new installation failed for both. Keep the extension and actual executable in the note before changing settings or reinstalling the program.
Use the documented association controls
mpv.net’s manual describes registration under its setup controls and a Windows Open with route. Follow the current instructions for the installed build and Windows version. Choose only the file types you intend to associate, preserving other household or work preferences.
If there are portable and installed copies, confirm the selected executable belongs to the copy you maintain. An association pointing to a removable drive or an old folder can produce a different issue from a missing association. Keep the old configuration available until the replacement is confirmed.
Verify the precise result
Close the test window, then open the same file through File Explorer again. Check the player identity and ordinary playback. If the file opens in mpv.net but will not play, that is now a media-support question, distinct from the successful application selection.
For support, provide Windows version, file extension, installed or portable type and the two launch outcomes. Hide private filenames where unnecessary. Avoid editing registry entries blindly or changing every media default to solve one extension. This article describes the publisher’s association distinction; it does not change settings or test a reader’s Windows installation.