...
rm /tmp/rialto-registry.bin ; GST_REGISTRY=/tmp/rialto-registry.bin RIALTO_DEBUG=5 RIALTO_CONSOLE_LOG=1 RIALTO_SOCKET_PATH=/tmp/rialto-0 XDG_RUNTIME_DIR=/tmp WAYLAND_DISPLAY=westeros-cobalt LD_LIBRARY_PATH="$PWD/usr/lib" COBALT_CONTENT_DIR="$PWD/usr/share/content/data" RIALTO_CLIENT_BACKEND_LIB="/usr/lib/libRialtoClient.so" gst-launch-1.0 playbin uri=file:///tmp/sample-video-file-for-testing.mp4
There is a small correction in the below "Run YouTube" Command mentioned in rdkwiki page
remove "$PWD" in COBALT_CONTENT_DIR
add "RIALTO_SINKS_RANK=0" to start playback in YouTube.
RIALTO_DEBUG=5 RIALTO_SINKS_RANK=0 RIALTO_SOCKET_PATH=/tmp/rialto-0 XDG_RUNTIME_DIR=/tmp WAYLAND_DISPLAY=westeros-cobalt LD_LIBRARY_PATH="$PWD/usr/lib" COBALT_CONTENT_DIR="/usr/share/content/data" RIALTO_CLIENT_BACKEND_LIB="/usr/lib/libRialtoClient.so" /usr/bin/cobalt_bin