macOS: GStreamer video sinks hang without NSApplication initialization in LGI

[andrewstarks]

Hi, I'm having trouble with a basic script on macOS. I also tried the Overview tutorial, which also doesn't work. I suspect support on the Mac is not available?

I created this issue report with AI help. My apologies if anything obvious is wrong. I am not fluent in GStreamer, at all. Just learning it for the first time.

Repro

Save this as repro.lua and run with plain Lua 5.3 on macOS:

local lgi  = require 'lgi'
local Gst  = lgi.require('Gst','1.0')
local GLib = lgi.require('GLib')

Gst.init()

-- Ensure LGI did _not_ expose macOS init helpers
assert(Gst.macos_init == nil)

local pipeline = Gst.parse_launch(
  'videotestsrc pattern=solid-color ! videoconvert ! autovideosink'
)
pipeline:set_state(Gst.State.PLAYING)

-- Block so the window would stay open if it appeared
local loop = GLib.MainLoop()
loop:run()

pipeline:set_state(Gst.State.NULL)

Environment

• LGI: 0.9.2-1 (installed via luarocks install lgi)
• Lua: 5.3.6 (built from source)
• macOS: 15.5 “Sequoia”
• GStreamer: 1.26.3
• Installed via Homebrew:

brew install gstreamer gst-plugins-base \
             gst-plugins-good gst-plugins-bad \
             gst-plugins-ugly gobject-introspection

Environment Variables

export GI_TYPELIB_PATH="$(brew --prefix gobject-introspection)/lib/girepository-1.0"
export DYLD_FALLBACK_LIBRARY_PATH="$(brew --prefix glib)/lib"

Output / Error

Running lua repro.lua prints:

GStreamer-GL-WARNING **: An NSApplication needs to be running on the main thread to ensure correct behaviour on macOS. Use gst_macos_main() or call [NSApplication sharedApplication] in your code before using this element.

and no window ever appears. The process hangs indefinitely until killed.

Expected

• A video window should open showing the test pattern and remain until closed or EOS.
• No GL warning should be emitted.

Workarounds Tried

• Switched between autovideosink, osxvideosink, glimagesink, and avfvideosink—all hang with the same warning.
• Verified the same pipeline works in gst-launch-1.0 on macOS and in Docker/Linux environments.

Request

Please expose the macOS initialization helpers in LGI (e.g. Gst.macos_init() and/or Gst.macos_main()) so that simple Lua scripts on macOS can start the NSApplication and drive video sinks without additional native glue.

[andrewstarks]

I think this is related: sdroege/gstreamer-rs#58