It is necessary, preferably by means of Qt , but it is possible with the help of other C ++ libraries to intercept the entire sound that applications emit, as for example Fraps does.

  • WinAPI, otherwise, to work with the Windows mixer, to catch the Master-Output (audio stream). - Vyacheslav Savchenko

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this is called loopback recording, a duplicate question on EnSO; an example link there too

in short - the Windows Audio Session API (WASAPI) is used, specifically about loopback recording