Hi,
subtitleoverlay is native gstreamer plugin and does not support NVMM buffers. Please try
gst-launch-1.0 subtitleoverlay name=ov ! autovideosink \
filesrc location=~/Videos/sample.mkv ! queue ! \
decodebin3 name=d d.video_0 ! 'video/x-raw(memory:NVMM)' ! \
nvvidconv interpolation-method=3 flip-method=0 ! video/x-raw ! \
videoconvert ! videorate rate=10.0 ! ov.video_sink d.audio_0 ! \
queue ! audioconvert ! speed speed=10.0 ! alsasink d.text_0 ! queue ! \
ov.subtitle_sink -e