What are the entire set of criteria that decide how 'b/v' are pronounced in Spanish?

I see here and here that 'b/v' are pronounced like the 'b' sound when it is the first letter of a word or when it follows a 'm' or 'b'.

However, the pronunciation of 'v' in 'vivo' is closer to 'v' than 'b' as seen here whereas it should be pronounced like 'bibo' based on the rule that I've mentioned above.

Is there any other rule that I may have missed?

  • V and B always sound the same (they're are no words for which switching the letters will change their pronunciation except for some English influenced dialects like PR Spanish where a small effect has been occasionally noted). The better question is how V/B sounds in a given position. – user0721090601 Dec 2 '18 at 23:25
  • 1
    I've reframed my question now. – n7rider Dec 2 '18 at 23:31
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