Improve CPU usage for linux capture #244

Job	Run time
build-linux (gcc-9)	6m 39s
build-linux-Qt6 (gcc-9)	6m 12s
build-macos-brew (clang-9)	4m 47s
build-macos-brew-Qt6 (clang-9)	5m 34s
build-macos-no-brew (clang-9)	10m 31s
build-macos-no-brew-Qt6 (clang-9)	12m 45s
build-windows-mingw (5.15.2)	7m 58s
build-windows-mingw-Qt6 (6.3.0, qtmultimedia qt5compat)	8m 17s
build-windows-vs (5.15.2)	8m 22s
build-windows-vs-Qt6 (6.3.0, qtmultimedia qt5compat)	12m 41s
	1h 23m 46s

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