This plugin allows embedding avplumber graph into OBS, as a source. You can use it as a replacement for ffmpeg_source (media source) for live video input (avplumber doesn't support seeking so it isn't that useful for media files).
It requires patched OBS. The patch was created for OBS 27.0.1 and wasn't updated since then. See obs_patches/hwaccel_async_sources.patch.
Patched OBS is required only because this plugin supports hardware-accelerated decoding and rendering on NVIDIA hardware, using nvdec/cuvid & CUDA, without frames leaving the GPU and wasting PCIe bandwidth (so called zero-copy). If you don't need this feature, you can strip functionality related to hardware frames in avplumber/src/nodes/obs/obs_video_sink.cpp. Start with class member obs_hw_ and remove code related to it.
pluginsrc=`pwd`
avpdir=$pluginsrc/../..
obsdir=$HOME/obs27
mkdir $obsdir
git clone --recursive -b 27.0.1 https://github.com/obsproject/obs-studio $obsdir
rsync -a $pluginsrc $obsdir/plugins/
rsync -a --exclude=.git --exclude=library_examples --exclude=objs $avpdir/ $obsdir/plugins/obs-avplumber-source/avplumber
cd $obsdir
patch -p1 < $pluginsrc/obs_patches/add_avplumber_plugin.patch
patch -p1 < $pluginsrc/obs_patches/hwaccel_async_sources.patch
and build OBS as usual.
Add avplumber source to some scene.
Paste content of examples/rtmp_input.txt to the script field in source properties, change input URL and confirm.
After a few seconds, you should see and hear the input stream in OBS.