How do some people "read lips"?

As someone who was born with unilateral moderate->severe hearing loss, I can read lips. The experience is likely unique across the hearing loss spectrum / time of onset, and some people may be able to learn that skill themselves, idk. I'm sure 100% deaf people experience it in their own interesting way.

To me it's not anything I conciously do, and it's not something that's really that visible to me. The fact I can still hear, but not as well as people with normal hearing affects how it works. The way I'd explain it for me is kinda like this:

Sometimes I can't hear enough to tell what is being said, one way my brain naturally deals with this is by reading the speakers lips and using that to help filter and understand what its hearing. I can kinda apply it as a skill, like with muted videos and people I can't hear because of distance, but it doesn't work that well and isn't worthy of trust.

So for me it's more of a sense, not something I do or think about. However, its basically the least effort way to understand speech that isn't clear enough. This is in contrast to another way I/my brain goes about it, which is trying really hard to figure out what it just heard.

To answer your last question, yes it is likely a mistake. Theres a youtube channel about that whole concept, called bad lip reading or something. They dub over video with audio that matches the lips well enough.

To put my experience into perspective, which might work for at least a few people: closed captions subtitles. I mean... I've never asked anyone else but yall arent just reading them, right? To me they just clarify the speech subconsciously (for the most part), rather than me reading them off the screen when I need them. Captions are weird... Who knows if this is accurate to my experience or similar to others.

It's inference based on mouth movements, but it isn't as rough as it seems like - context plays a huge role on disambiguation, just like it would for you with homonyms that you hear. It's just that the number of words that look similar when you mouth read is larger than the number of words that sound the same, since some sounds are distinguished by articulations that you can't immediately see (such as [f] vs. [v] - you won't see the vocal folds vibrating for the later, so "fine" and "vine" look almost* the same.)

Also, the McGurk effect hints that everyone uses a bit of lip reading, on an unconscious level; it's just that for most of us [users of spoken languages] it's just to disambiguate/reinforce the acoustic signal.

*still not identical - for [v] the teeth will touch the bottom lip a bit longer.

I think exact is impossible but I think with enough practice you can get pretty good at identifying words. A good example of lip reading for false words is Bad Lip Reading

No hearing loss here, but I'm semi-alright at reading lips. It's somewhat of a guesswork, but you can make out a decent amount of info, depending on how clearly the other person enunciates their words.

I suspect most or all people already do lip reading to some extent, but you can definitely "train" yourself to read lips better.

I mainly look for consonants since those are the easiest to identify (the shape you make when you make an m sound looks super different from when you make a t sound, for instance). There's a slight bit of guessing involved, since several consonants have the same mouth shape (m and b, for instance). Sometimes, vowels can throw you a bone and be really easy to read (the a in apple, for instance, has you open your mouth very wide), but I generally struggle to read most vowels. The rest is just piecing together what was said based on context clues.

I've heard that it's easier if you're familiar with the person, past that I'm curious too!

As a linguist, I suspect that everyone lipreads to some extent as a conversation repair mechanism. Accuracy probably depends on skill and context. Family members with hearing loss are pretty good at understanding a speaker that they can see clearly, even when there's no sound information available at all.

I can't do it at all, scouring this thread for tips. I suspect it is pattern recognition my brain has not yet been trained to do.

Hearing loss my dude. Army. Necessity is the mother of invention. It makes date night fun with my partner though. I can read and sign remote convos to her and sometimes that's spicy/fun. It's not perfect but I can usually follow the thread. More so if the target is animated/angry/excited. Unfortunately the best ones are the hardest. We love the first date awkward convos, the public breakups, and admissions of guilt but those tend to be subdued and difficult. When you get them though it is choice.

All I know is that when people started wearing masks, suddenly I had trouble understanding them. I guess I'd picked it up subconsciously alongside my hearing loss.

Seinfeld had an episode that revolved around lip reading.

https://youtube.com/watch?v=BxNl8VQ6tPk