Geoffrey

As far as I can tell...
If the face moves out of the focus area, their face will still be "tracked," meaning their will be a white box around the faces (or faces if there are more than one person in the shots but no in the AF area), but the autofocus will give priority to what is in the AF area box. 
why use it? 
Say you are holding doing a product review in your living room and the camera is focusing on your face. You hold up a nice shiny lens / camera / whatever in front of your face (obscuring your face) and the camera should focus on the item.
With the Human Detect AF, the camera MIGHT focus on a photo on the wall in the background of someone's face. 
I don't think it is a night-and-day difference in terms of accuracy. But more of a backup. If the person puts on sunglasses or a mask, or their are shadows falling on their face, or for some reason the AF system stops recognizing their face as a face, then if they are still in the AF area box, the camera will still focus on them. 
Also - and I have zero proof this is the case - I think that using the AF One Area just helps the camera AF system "concentrate" as it were. I don't know the scientific / engineering terms, but just that the AF system is less likely to get distracted.
I don't want to get too negative on the system. Josh Cameron makes a lot of videos about the S5 and S1, and he seems to get good results using continuous autofocus with the 20-60 and 24-105 lenses. There are a few others that seem to be able to get usable results. There are many times when 85% is going to be more than good enough.
For my needs, if I really need something to be in focus, I just have to go with either AF-S or manual focus for now. I would love to pick up a prime like the 24mm for use on a gimbal shooting 4K 60fps (which is in aps-c crop mode) and use it in af-c, but I am a bit reluctant to buy L-Mount glass if the AF isn't going to be improved significantly through updates (or new camera models).
And as @MrSMWmentioned with his S1H, I would just set up my S1 as either manual focus (or single af) on a tripod, press record, and walk away, letting it record long events / interviews from a static angle. 

It might depend on how the AF is reacting to the subject you are shooting.
If it is pulsing, then you would want to turn the sensitivity and speed down. 
Also, for the best results I have gotten from continuous AF, I usually use one-are (or one-area plus) and turn on face detection. 
If you are using the first AF mode, which is face recognition, you should either tap on the face you want to track, or use the joystick and push in on it to track that particular face. (the same thing for the Tracking AF mode, although I don't find the tracking AF mode all that reliable at all).
You want to "confirm" the face by tapping or using the joystick push in (as mentioned above) in case there are multiple people in the frame and then the camera will know whose face to focus on.

Well yes it does close the gap faster but I think because you are moving, the lock on the subject seems to stick better maybe because since you and the camera are moving it is keeping check on it more? Might just be luck though but I like the effect anyway. But I do admit, because I am relatively new to using CAF, I have less high expectations of its capacity perhaps. One thing that has helped is that lock on the subject you can do that the video outlined some pages back.

Given your experience here - do you have preferred CAF settings (I mean the fine tuning settings deep in the menu)? EDIT: apologies I just see you have already posted these. Very useful, thanks. I shoot 50p (1080 - don't have the gear for 4K editing) so that is good.

It's probably fine for holidays. Although If I had young children around three or four, I don't know how good the AF would be at following them around. I am sure that my significantly older Sony a6500 or Olympus E-M1 MK II (with firmware 3.0 or later) would track them FAR better. 
Is the S5 a professional camera? Well, I would say there a significant amount of professionals using it to make money (including yours truly), if not as an A cam, at least as a B or C cam. It is a good jack-of-all-trades camera, IMHO. If the continuous autofocus was brought up to the level of Sony or Canon, or the new OM-1, it would be an absolutely great camera.
Paul Byun has made a couple of good videos about his experience as a commercial videographer using the Continuous AF and he has found it useable, but he has made some compromises that, to be honest, kind of offset many of the great benefits of shooting on the S5 or S1 cameras (e.g., shooting at 60fps, shooting in aps-c crop mode, shooting in a profile with higher contrast, shooting on primes at f/2.8 instead of f/1.8, etc.,).
So they aren't terrible cameras, and as you said, work great for non-critical work. But they really are just a reliable continuous autofocus system away from being the perfect camera (at least in my experience).

Hey, no problem Geoffrey, - it's OK to have a different opinion and express it.
I've explored every single setting and then some and in my experience, in regard to tracking people walking towards you at anything above even a moderate pace, it's not reliable.
Arguably, no camera is 100% reliable, but in my experience, the XT3 was better than the S5 is and neither are as good as the Nikon Z6 I tried and that isn't as good as anything Sony or Canon.
But the S5 still remains my main video tool for professional work.

Yeah, understood. I admit to having little experience on other cameras with CAF (or V-Log) but have read the Sonys are 'better' but I do wonder how much better in the conditions you describe (V-Log etc)? If 85% = 0%, in effect for certain situations, what percentage success is OK, as none of them work 100%? We do ask quite a lot of these machines!

My impression from the OP was they wanted a cam for holidays and stuff and I would say the S5 CAF is totally fine for that (yeah you get a bit of pulsing too but not much and only really notice it if you look for it which most people wont). Maybe this is the difference - total professional reliability versus more general use, use where some technical failures don't matter. The question I would have there, is the S5 a fully 'professional' camera to be totally relied on? Given the price, I would say it is definitely not and so should be judged accordingly

I have been using the S5 human detect continuous AF quite a lot recently. I shoot using the CineD2 profile (standard kit lens) and mainly outdoors, hand held. It works pretty well and am a bit baffled by the criticism it gets here. Maybe that is because people expect 99% success with it when in reality it is more like, I dunno 85%? I suppose with crucial commercial shoots this becomes an issue. But, with practice you get to know when it falls over - mainly too dark or too bright and movement is too rapid (so practice with it really does help like most things). Avoid that and it works the vast majority of the time very well and I love the look it gives. In fact as I have got experience with the S5 generally, I have grown to love it more and more, faults and all.

I have been using the S5 human detect continuous AF quite a lot recently. I shoot using the CineD2 profile (standard kit lens) and mainly outdoors, hand held. It works pretty well and am a bit baffled by the criticism it gets here. Maybe that is because people expect 99% success with it when in reality it is more like, I dunno 85%? I suppose with crucial commercial shoots this becomes an issue. But, with practice you get to know when it falls over - mainly too dark or too bright and movement is too rapid (so practice with it really does help like most things). Avoid that and it works the vast majority of the time very well and I love the look it gives. In fact as I have got experience with the S5 generally, I have grown to love it more and more, faults and all.

This is a strange one and I suspect no-one will have come across it but I was doing some recording the other day using a Zoom H6 and the S5. I used the line out of the Zoom to connect into the camera so I had a guide track for synching the zoom audio in post. The Zoom line out is specifically designed for such a scenario (stated in the manual). But here's the thing, after careful tests and some head scratching I came to the unavoidable conclusion that the phase on any input into the Zoom was inverted once it is laid down as the S5 audio track.
The cable is an unbalanced 3.5mm so it cannot be that so that leaves either a problem with the Zoom line out (unlikely) or the S5 line input (more likely). Either way this is clearly a factory fault. There is nothing that can fix this at source and it is easy enough to invert the phase in post, and in fact mixing both signals in any final project is very unlikely anyway, but still, it should not be happening.
One other fairly obvious observation is that the noise floor of the 55 is noticeably higher than the Zoom which is pretty pleasingly quiet. This is not helped by the fact the Zoom line out is fixed at -10dB so you have to have the S5 at 0dB input at least. Anyone who cares about sound quality and is recording in a quiet environment would do very well not to use the S5 for sound unless you have a high quality mixer that enables you to lower the S5 input level to -6dB at least..

I use this all the time, I shoot about 10+ fashion shows a year and as a OMB I am commissioned to do both the photography and video so for the walks there's really no other way to do it. I also use this to punch in and out when doing an interview without using two cameras. I will frame it so that its a medium wide shot at 4K but later I can punch in to make it a tight shot. 
The only annoying though is that without CAF you really need to nail that initial focus manually and use a wider aperture such as 4.0 to ensure that the subject is still in focus if they move forward or backward slightly. I have shot razor thin before at F1.4 but with that tiny screen and no CAF its pretty much impossible to keep the eye in focus if the subject moves at all.

I have a more general basic question for those experienced in such things.
Watching live TV panel interviews the other day I was wondering how they do the thing where they cut between a wide shot of the interviewee and close up of the same person but with exactly the same angle of view. It looks like it is the same camera as the angle is identical and this is why it works, rather that being a jump cut (I mean it sort of is but does not jar). Is it some kind of auto zoom that can be clicked when desired or is it two cameras somehow positioned so the angle is the same, and the cuts are done by the director in the control room? 
It is a very simple, standard technique but it occurred to me I did not know how it is done and it would be a useful thing for me on a project I am working on right now.

Thanks for this thread - exactly what I am grappling with at the moment.
Right now I use a Sanken radio mic / Sennheiser setup for the mono voice (moving around freely outdoors) and a spaced pair of DPA mics mounted on the camera on a bar. All mixed in the field via a Juiced link 4-channel mixer mounted below the camera. I can easily use it all hand held and have great freedom moving around which is what I need (having separate devices, trailing leads etc would make life so much harder and in the end, worse footage as a result). The setup works very nicely and gets a wide ambience and nice focused vocal which is what I want ... but phasing issues occur especially when I get closer to the Sanken mic and it can compromise things in a way that annoys.
I need to solve this rather unpredictable problem and the most obvious thing is to replace the A/B DPA pair with an XY mic, so the info on this thread is invaluable. From what I have read, the SVMX or AT8022 look like the best bet. The Sanken CMS-50 looks lovely but the price is way above anything else and too much for me but maybe the BP4025 is also in the running here.

Do let us know how you get on with the SVMX.

Thanks for the advice re autofocus testing
And yes I have one of the top function buttons assigned to peaking - I had just never noticed the P going on and off., till now!
On a tangent, I am finding the CineD2 profile really nice for autumnal colours. My new favourite. I have also gone back to doing everything in HD as I just don't have the storage and power for editing 4K. Plus HD on the S5 looks great anyway. Interesting watching Andrew's video on the main forum page about the obsession with tech and I would add obsession with pixel count to that.

Yes I mean in human / animal mode. I have tried this but not had any joy but then I have found once the yellow box appears it works anyway (but the suggestion in the video is it could work better). It is almost impossible to test without another human subject but I have a shoot on Thursday. Have you used the method when there is only one subject so nothing to choose from?

Simple question, in Movie mode what does the P (in a box) to the right of MF on the LCD mean (also get it with AFS but not AFC which displays the AFC type instead)? I have scoured the manual and come up with nothing. 

And I got mine back from the menders, and finally it is working fine again. Now to get used to it all for a second time.
Shame you couldn't get round the focus issue thehebrewwhammer but sometimes you have to just accept something isn't working for you.

Update on my broken S5 that no-one will be interested in:
Finally got it returned. Screen fixed. Gave it a test run and . . . none of the buttons on the back except play and veiwfinder buttons work any more including the focus type switch!! The camera is now totally useless. Can't believe it. 
Rang the repair company direct and they were surprised but at least contrite and back it will go. I suspect there is some small connecting wire they forgot to re-attach but then didn't think to press any of those buttons to test it since the screen works fine (and all the buttons and wheels on the top).
I did enquire of the company I bought it from that really I should be able to ask for a replacement camera. They agreed but claimed stocks are non-existent and supply times for new stock is months away, all due to the pandemic. Do I believe that? Dunno but I decided pushing it would only stress me out even more so repair again it is. 
Sigh.

Update on my broken S5 that no-one will be interested in:
Finally got it returned. Screen fixed. Gave it a test run and . . . none of the buttons on the back except play and veiwfinder buttons work any more including the focus type switch!! The camera is now totally useless. Can't believe it. 
Rang the repair company direct and they were surprised but at least contrite and back it will go. I suspect there is some small connecting wire they forgot to re-attach but then didn't think to press any of those buttons to test it since the screen works fine (and all the buttons and wheels on the top).
I did enquire of the company I bought it from that really I should be able to ask for a replacement camera. They agreed but claimed stocks are non-existent and supply times for new stock is months away, all due to the pandemic. Do I believe that? Dunno but I decided pushing it would only stress me out even more so repair again it is. 
Sigh.

Yes, audio is as much of a discipline as video and of course normally it is done by a dedicated person, so having to do both is a tall order for anyone. Plus what you have to do is taxing of itself - having to pick up intelligible and clear speech from various individuals, ambience etc. It is one of those truisms too that bad sound will be rejected by the public much more readily and quickly than dodgy images. I don't think the sound on the Panasonic module is bad btw, I just have a much lower tolerance as a sound person. I suspect most people would not notice what I do. One test you could do if you haven't done it so far is to plug headphones into the cam (in a very quiet environment) and ride the audio outputs on the cam and XLR module and find the settings that produce the least hiss which I very much expect would mean lowering the cam record input.

No problem. I'm unsure about the S5's hertz settings. I know there were some issues with other Panasonic cameras when you set to true 24p but since you're set to Pal/25p I don't think that should be the problem then. Are you noticing the flickering with all lettering, or just on letters/numbers on electronics?
vLog is a nice profile and since the S5 uses the full log profile, it should be pretty good. But Panasonic has a couple nice profiles that can be a bit more forgiving and still offer a bump in dynamic range. I always liked Noam Kroll's settings for CineLikeD and Like709 seems to be pretty nice as well.
But don't give up on VLog yet. The S5 has Dual Native ISO, so if you set to the higher ISO in lowlight, then that should help with the noise. Then you can either stop down, or use an ND to lower your exposure. 

Thanks for the reply mercer - I have a lot to learn about V-Log I think. It might not be for me but I was drawn to it because the flickering I mentioned did not occur when I shot log. Can you set the Herz rating of the S5? I cannot find anything about that. I am PAL land so use 25 / 50p  I did wonder if the problem was due to the artificial light - not fluorescent though, LED standard (modern) lightbulbs.

I was thinking something along those lines, like the phantom power should be turned off first. That's why I think I should read the manual to see if there is a startup sequence. I just don't remember these problems with the GH5 but of course there could be different tolerances with the S5.
 
I have the Sigma EF adapter and EF mount lenses so it may work slightly differently with L mount lenses. But for me, I keep the dial in Movie Mode (M with the little camera beside it), the EF lens is set to AF on, and the back button focus selector is set to S(ingle) or C(ontinuous). Continuous AF doesn't work with the adapter, so when you have the adapter mounted and an EF lens attached S and C does pretty much the same thing. You can also use M but then you can't use the half press method to AF. So the three different ways you can use Hybrid One Shot AF with the S5 that I have found is:
 
Focus Mode Dial set to S or C- The EF lens has to have AF turned on (switch on the lens) and the top dial in Movie mode. With it set this way I can then half press to AF both while recording or before starting to record. I typically pick 1 area for my focus mode. Focus Mode Dial set to M - The EF lens has to have AF turned on and the top dial in Movie mode. This is where it gets interesting. With this combination of settings. half pressing the shutter button doesn't do anything, the only two options are to turn the focus ring to manually focus, or you can tap the screen where it says AF and it will focus one time for you. What I like about this mode is for the EF lenses that support it, the camera will automatically punch in to help you MF when you turn the focus ring on the lens (as long as you set it up to do this in the menu and as long as you haven't yet pressed record). For the other two modes, if you want to punch in to check focus you have to press the center button on the focus mode selector switch.  Lens AF Mode Off or Fully Manual Lenses - If you switch the lens AF mode to off, then you are 100% responsible for pulling focus. What is pretty cool about this mode is that the focus selector switch doesn't matter anymore. S/C/M all automatically punch in to help you set focus as long as you have it set that way in the menu and as long as you haven't yet pressed record and as long as the lens reports to the camera that the ring is being rotated (most of my lenses do). I'll admit I've gotten kind of lazy with focusing now that I have the S5. With the GH5 all of my lenses were manual so I used to have to focus everything by hand. With the S5, the focus peaking is so hard to see (IMO worse than the GH5), that I've found manually focusing much harder so I tend to rely more on the hybrid method. The only problem is the camera completely fails to focus sometimes in this mode so then I still have to do some manual focusing.
 
I like many others truly hope Panasonic does something to improve their AF. I would literally buy an S5II if the only improvement was a working AF system.

On the S5 there is a dedicated AF ON button on the back of the camera. One-shot AF is the way I think about it. I find it essential as the screens are small and focus peaking not that great (though that can be useful it depends on the light) plus my eyesight is not that great these days!

Do you mean use the autofocus button when in MF? If so then yes, I use this method all the time when shooting video. You can also use the MF ring when in autofocus.

I used to use a Canon XM2 (miniDV) and really liked it - very pleasing image. It had a fun, adjustable strobe effect too.