I've got a question about the effect of the séimhiú on the pronunciation of m and b. This will obviously differ for Munster/Ulster Irish but here goes...
When do 'mh' and 'bh' create a /w/ sound and when do they create a /v/ sound? Are they always interchangeable? Does it depend on the vowel? Or the canúint? Or the position in the word?
For example... mo mhála, a mhúinteoir, Contae Mhaigh Eo. I've heard /w/ and /v/ for each of these before.
My name is Brian so I hear "a Bhrian" regularly but I've never heard it pronounced with a /w/ sound. (Though that could be because Irish may not allow for /wr/) That said, I would only use a /w/ with 'go bhfuil' and I've definitely heard it with "an bhfuair tú?".
As regards word position, from my time up in Donegal word final 'mh' and 'bh' was never almost pronounced /v/ and had a sound much more similar to an approximant /w/... /du/ for 'dubh, etc.
"Ar mhol sé; an mhonarcha?" - can these both be /w/ or /v/, or only one of them?
"An bhfaca tú dath an mheaisín?"
"A Mhíchíl, an bhfuair tú ár bhfíon, a mharmaláid agus mo mhadra ón bháicéir?" (Ha, I'm stuck for nouns!)