Add concurrent video playback limitation

[CAZ-H]

Changes

Currently, there is a warning that will be output when you try to play more than 2 videos at the same time. This is a blocker for some interesting uses of this feature (e.g. Times Square style billboards, video ads in bus stops, etc.) that developers should know ahead of time.

Given that this feature is new-ish and might still be subject to fine-tuning, I'm not sure if it's valid to document these limits. Feel free to reject this change if these limits are still actively being assessed.

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