Antivirus

How is the prefix "anti" usually pronounced in the USA? What about "semi"?
I think I usually hear "an-tie" and "se-my" before consonants, and "an-tee" and "se-mee" before vowels. Does that make sense? If so, it should be "an-tie-virus", "an-tie-chinese", "se-my-vowel"... and on the other hand "an-tee-abortion".
Any advice for me? Thanks.

Around here in southeastern Wisconsin, "anti" is normally [ˈɛ̯̃æ̃ɾ̃a(ː)e̯] and "semi" is normally [ˈsɜ̟̃ːma(ː)e̯], but there are just particular words in which these vary in an unpredictable manner. For instance, "antiseptic" is [ˌɛ̯̃æ̃ɾ̃ɨˈsɜ̟ʔptɨʔk] here. Note that such is common in English in general, where different words will have etymologically identical affixes being pronounced in different manners which are not predictable but rather have to be learned individually.

I gernerally pronounce them [ænti] [sɛmi]. I'm not aware of a prevocalic versus preconsonantal distinction; I would use [i] in all your example words. I was wondering if [aɪ] was more popular in Britain, but the Cambridge Online Dictionary seems to show a preference for [i].

I use [ænti] for anti. I also have [i] in all of the other variations. I believe that some use [aɪ] when they want to add emphasis, but it seems that [i] is more common among native English speakers.

On another note, I always use [ˈaɪðəɹ] for "either" and [ˈnaɪðəɹ] for "neither".

I found an old thread here where "anti" was discussed, and it seems to me there's no agreement, so both seem in use in the US, and there's no way to find out which is the most common. I heard "antivirus" in two video on Youtube, pronounced by Americans, and one said an-tee, and the other an-tie. So... I'll have to pick one at random, I'm afraid.

An'tie' sounds horrible to the British English ears.

Always /ɪ/ never /aɪ/ for both in Australian English. I'd always thought it was the same for all non-North-American dialects.