Garbled composite output from Pi3b

[Kapcaniew]

Hey guys,
I've just got my Pi 3b to output PAL via composite, but something has gone wrong. It's a direct screenshot of what I'm getting on the screen.

WIN_20200508_21_41_20_Pro.jpg (36.46 KiB) Viewed 252 times

Has anybody seen such a thing? The Pi is (temporarily) connected to a PC by a chinese knockoff "EasierCAP" USB dongle, but I doubt that it's the adapter's fault - I've been using it with a few different sources (cameras, VCR, canon dslr) and only the Pi signal is acting up.

Eventually I'm going to connect this Pi to an old 5" b&w CRT tv set (which I don't have yet and I wanted to test the composite out on something), so if the problem lies in this garbage adapter then I won't even waste time trying to get it to work. Any clue what might be causing this issue?

[mahjongg]

Yes, the video signal is inverted by exchanging the ground and signal leads.

Its described here:
viewtopic.php?p=653422#p653422

you need another video cable.

[drgeoff]

Yes, the video signal is inverted by exchanging the ground and signal leads.

Its described here:
viewtopic.php?p=653422#p653422

you need another video cable.

The video is NOT inverted. Unless there is another inversion in the Easycap dongle or software there is nothing wrong with the cable plugged in to the RPi.

There is a sync problem, but I cannot diagnose where from the info available.

[hippy]

Raspberry Pi composite video has always been a mess when fed into my PVR but is fine when going direct to my DVD player displays and TV. I never investigated why or what it is which prevents the PVR accepting the signal - that works with every other composite signal I have fed it.

TL:DR - That it doesn't work with your capture card doesn't mean it won't work with something else.

[Burngate]

My take on this:
The dark green vertical stripe is the colour burst.
The horizontal sync pulse should form a blacker-than-black (less than 0v) vertical stripe to its left.
All of that should be in the blanking area, at 0v

None of that is there - instead the blanking area is above 0v, so grey compared to the darkest bits of picture.
And the sync isn't there.

But your PC seems to be finding something to lock to, so your "Chinese knockoff "EasierCAP" USB dongle" seems to be moving the sync pulses to where they shouldn't be. We used to do that on purpose when we wanted to check they were in spec., but why it's doing that ...

[drgeoff]

My take on this:
The dark green vertical stripe is the colour burst.
The horizontal sync pulse should form a blacker-than-black (less than 0v) vertical stripe to its left.
All of that should be in the blanking area, at 0v

None of that is there - instead the blanking area is above 0v, so grey compared to the darkest bits of picture.
And the sync isn't there.

But your PC seems to be finding something to lock to, so your "Chinese knockoff "EasierCAP" USB dongle" seems to be moving the sync pulses to where they shouldn't be. We used to do that on purpose when we wanted to check they were in spec., but why it's doing that ...

I did initially wonder if there was a "pulse cross" facility on the display software that had been selected but I wouldn't expect to find such a facility on non-pro equipment.

If you look very closely it is only the horizontal interval that is messed up. Blacker than blacks are present in the vertical interval. See my enhanced version where the broad pules and equalizing pulses mid line are easily visible.