It was a long time ago when I compiled it for my Mac, but I guess with MacPort or homebrew, using the same method as for linux.
Get the source of Gem from the github, and just compile it after installing libvlc-dev.
I think that is the whole philosophy behind it.

On Thu, Nov 22, 2018 at 9:30 PM Johnny Mauser via Pd-list <pd-list@lists.iem.at> wrote:
Somehow i never got the vlc plugin to work. How do you do it? Can someone enlighten me?

Am Do., 22. Nov. 2018, 17:01 hat Jack <jack@rybn.org> geschrieben:
Good to know ! Should be useful for OSX users.
Thanx.
++

Jack



Le 22/11/2018 à 16:27, Csaba Láng a écrit :
> Just to make for others easier in the future, managed to have a video
> input from a webcam into Gem on Mac OS X 10.14 with the VLC plugin,
> which I admire very much :)
>
> Opened vlc first and added a Capture Device, which opened immediately
> the webcam with a tytle of the window on the
> top: qtcapture://0x14100000043e3009.
> So sent a message to pix_vlc: device qtcapture://0x14100000043e3009 and
> tadam there is the live input from the webcam.
>
> What is even better that I can use the same stream twice, once to VLC
> and simultaneously into Pd as well.
>
>
> Thanks for all the info you gave,  that is why I love this community!
>
> Best,
> Popesz
>
> On Thu, Nov 22, 2018 at 4:17 PM Csaba Láng <langcsaba@gmail.com
> <mailto:langcsaba@gmail.com>> wrote:
>
>     Perfect, thanks Jack, was looking for this page just could not find
>     in the deep noise on the mighty internet!
>
>
>
>     On Thu, Nov 22, 2018 at 4:15 PM Jack <jack@rybn.org
>     <mailto:jack@rybn.org>> wrote:
>
>         To use VLC backend with [pix_video] :
>         - send [driver vlc(
>         - then send a message [device ...(
>
>         where ... are instructions to use this backend. Explainations
>         are here :
>         https://wiki.videolan.org/VLC_command-line_help
>
>         For exemple to capture your screen, you can send [device screen://(
>         ++
>
>         Jack
>
>
>
>         Le 22/11/2018 à 15:51, Csaba Láng a écrit :
>         > Dear List,
>         >
>         > I am still looking for a reasonable solution to have a video
>         input to
>         > Mac OS X with Gem.
>         >
>         > I was testing syphon_client, works almost OK, except that
>         could not make
>         > any motion detector out of it, no pix_background works with
>         it, cannot
>         > change contrast, threshold, basically nothing.
>         >
>         > Just came to my mind the VLC plugin, which I have compiled
>         luckily, but
>         > the documentation is so poor to the VLC plugin that cannot
>         find a way to
>         > get a video device with one message into it.
>         >
>         > Can anyone give me a nice hint to use the vlc plugin with a
>         USB webcam
>         > connected directly to the computer? What is the message to use?
>         >
>         > Thanks in advance for any help!
>         >
>         > Popesz 
>         >
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