The inputs 1-3 on the V-4EX only support 480P/576p. Input 4 supports up to 1080p. It's likely that what your sending out is a resolution higher than 480p/576P into inputs 1-3. Try them into Input 4 it should accept what you're trying to send in. You can read more about the resolutions accepted by the V-4EX in V-4EX accepted resolutions article.
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