When I scan a verse, I simply leave out elided vowels: I don't pronounce them at all. But I've heard theories that the Romans did pronounce them, but just as very short vowels of half a syllable's length. What do we know about this? Is there consensus about the pronunciation?
This is discussed in great detail in Allen’s classic Vox Latina ch. 4. His conclusion is (briefly) that a final short vowel followed by another vowel in the next word was elided (elisio), but a long vowel in the same position was reduced to a semivowel (synizesis).