Awesome achievement, it's really great to see this thread alive.
If I'm not mistaken, that video recording/playback never worked on this device so far (although video itself works). Finding a solution would really complete the work so far.

Video recording works/worked on 2.0.4.13 and 2.0.5.something, although you need some tricks and is not reliable.

I agree. Video recording/playback works fine on these versions 2.0.4.13, 3.0.3.9 and 3.2.0.12.
The video playback works on my image too but only in Kodi.
In the built on video player, it doesn't work.

Probably if I solve one of them (recording or playback) it will solve the other too.

In my image (wip0.16) the camera works only for making pictures.
If I switch to video mode, the back camera show the image but freezes when I hit the red button. For video recording the back camera shows only a black screen and the red button doesn't function.

So far when the camera is launched from console, these are the error messages I saw:
1. Switch to front camera (video recording):
and

2. Back camera, hit the red button to record a video:
Tried to google, but didn't find any obvious answer.
Tried to copy over the camera config files from the working 3.2.0.12 version, but didn't help.

I am still working on it.

Did you try to use another application for taking pictures/ video recording? I use Camera+. Of course, I doubt it will make any difference

Yes I did. The same result. Something is missing or needs to be updated (like for the date & time issue) but I don't know what.

In wip0.16 I spotted a serious problem.
Today it happened multiple times. Somebody called me and we didn't hear each other.
It works when I make a call, but it isn't always when I get a call.

Plus during the call I switched to the loudspeaker, and from this point the phone was randomly automatically switching between the ear piece and the loudspeaker. Hmm.
It seems need to go back to the drawing board.

Edit: In this minute my phone just started to play the ringtone. The screen was blank and there was no incoming call. I couldn't stop the phone playing the ringtone because seemingly there was no reason why it started.
I restarted the network but didn't help. I needed to restart the phone to get rid of it. Strange. Oh my, I thought I had only the video recording to fix.

Sorry, I missed to respond on this one.
The problem is when I try to play an mp4 video with the native media player, the video playing doesn't start. However the same video can be played without any issues with Kodi.

@mautz
I have been thinking about the recently discovered audio problems related to the phone calls.
In my previous builds this problem was not there and I remember that I adopted your
/etc/pulse/arm_msm8974_hammerhead.pa file from your config.

Could you let me know what is this file and why it was necessary for your config, please?

Thank you.

I think the video recording/playing and the sound during the incoming calls issues are somehow connected.
I have identified a common error message 'shared memfd open() failed: Function not implemented'. Maybe this is a red herring again, but I have a feeling that if I find a solution to this error, that will fix both problems.