On the TX2 there is gstreamer0.10 or gstreamer1.0. It is supported on gstreamer above 1.0. Will upgrading to gstreamer 1.6 for example work as efficiently on the TX2? With the proper use of the hardware encoder?
Stop it with ctrl-C before it fills your disk. Right-click/Properties/Video on the file with nautilus (ubuntu file explorer) and you’ll see MP2TS as container.
AFAIK, you can only use matroska or mp2ts as container for h265 from gstreamer. For h264, you can also use quicktime container with qtmux.