How do pro animators properly produce lip-sync animation?

Hi. I should know this, I was an animation student years ago, but at the time I was using old-fashioned, traditional animation tools and equipment. This was back in the mid- to late-'90s; cartoons were still being made for the most part the old-fashioned way.

I remember when I was learning how to produce animation in art school, we recorded vocalizations on brown film. We listening to it by playing the film back manually frame by frame using some kind of old-fashioned film equipment. I don't remember what that machine was called, but I do remember isolating frames where the sound was recorded on the film and marking the frames off on the film with a yellow grease pencil. We broke words down by syllable and we were able to determine how many frames of animation we needed for each syllable. We are able to indicate where the syllables began and ended for each word, which was important, because we needed to know how many frames of animation we needed for characters' mouth movements. We marked all this off on animation production sheets. Using this info we could also determine what mouth shapes we needed to animate to form the words.

This gave me some idea of how lip sync animation was made, but I wasn't a professional.

Before the advent of digital ink and paint and other 2D animation software that is commonly used now, how did pro animators properly produce lip-sync animation?

How do most pro animators who produce cartoons in studio for TV and film do it now?

I've seen videos online in which animators demonstrate how do produce lip-sync animation using software like Flash for example. I don't know if the people in these videos were pros or not.

Please help. Thank you.