Hi Alexsander,
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Background video has always caused issues and is not all that reliable. This feature really could do with some major work, and until that happens I don't think it will work on windows.
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It depends on the power of your computer, but adding shadows and outlines to your text can slow down slide changes. Generally the more text you have on a slide, the longer it will take to change.
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Unfortunately both of the issues you have raised are limitations with the software we use to make OpenLP. This software is due to be upgraded after the next major release, so hopefully we might be able to make some improvements in these areas.
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Phill