Translation:Flies often live for one thousand hours.
Not really but in this case yes.
I really did not want to complicate this in my answer to you, because it is quite complicated. That's why I did not mention the dialectal forms. Remeber that the famous painter is named Mucha.
Also, you have to distinguish pronuciation and dialects. This issue is about dialects, not pronunciation.
Most sound changes radiated from the region around Prague and the peripheries of Bohemia or even separate regions like Moravia got them later or not at all. That's why Old Czech múcha changed to moucha in Bohemia but not in eastern Moravia.
And this was a regular sound change, it affected all words. múka -> mouka, lúka -> louka, ústa -> ousta
Originally, a poet in the 14th century asked: Noci milá, pročs tak dlúhá? But later we would say it: Noci milá, přočs (proč jsi) tak dlouhá?
So in Moravia they kept múcha and shortened it to mucha. Be aware that in northern Moravia and Silesia they stopped distinguishing long and short vowels altogether.
However, after certain time (say from 16 century onwards), the new changes (still mostly appearing in central Bohemia) didn't make it into the Standard Czech as defined in the 19th century. So most people in Czechia, and almost all in Bohemia, now speak Common Czech that will be the topic of the last skill of this course. It contains the innovations that did not make it into the Standard Czech but most people use them when speaking.
In Moravia, though, they kept their specisl dialects for a ling time but with the mobility in the late 19th and the 20th century they are merging and blurred. Instead of many distinct dialects we have a few dialect groups and most people do not use pure dialects any more and often use Standard Czech for speaking (unlike in Bohemia).
And some innovations were actually reversed. This very ú -> ou change became reversed at the beginning of words so you now have úředník even though people used to say and even write ouředník (hence many poeple's names and hence colloquial words like ouřada, ouřad). The new ou returned to the original ú at the beginning of the word. And we now have ústa and no ousta.