Hi,
x264enc is SW encoder in gstreamer:
https://gstreamer.freedesktop.org/data/doc/gstreamer/head/gst-plugins-ugly-plugins/html/gst-plugins-ugly-plugins-x264enc.html
It enables AU demiliter by default.
We verify below steps on r28.2.1/TX2 and it works:
// generate video files and playlist
$ gst-launch-1.0 videotestsrc num-buffers=300 ! 'video/x-raw,width=1280,height=720' ! x264enc ! mpegtsmux ! hlssink
// You should see
-rw-rw-r-- 1 nvidia nvidia 155 Sep 28 08:28 playlist.m3u8
// and
-rw-rw-r-- 1 nvidia nvidia 2738032 Sep 28 08:28 segment00000.ts
// run http server
$ python -m SimpleHTTPServer
Serving HTTP on 0.0.0.0 port 8000 ...
// Open link on iPhone 6 Safari
http://<TX2_IP_ADDR>:8000/playlist.m3u8