DVR + HW Transcode = buffers a lot. any recommendation?

I newly installed new tuner on my Intel N3700 + Windows Server 2012 machine,
and turned on DVR with HW Transcoding option.

With any client (which can watch DVR), I’m suffering with ~10s of buffering delay in every 20~30s when watching live TV with transcoding in any bitrate setting (even with <360p).
Surprisingly, it can handle SW transcoding well enough w/ 100% CPU usage and it shows no buffering.
Also fine with original quality when enough bandwidth is available.

Is there anyone can find something wrong with my setting?
Is this sort of HW transcoding limitation of my CPU/GPU?

FYI, most of H.264 HW transcoding of my library is fine.

Medias are mpeg2video?

The reason is that plex doesn’t support yet mpeg2video hardware decoding. Until devs activate it, there is nothing you can do. Hopefully, they will add this support soon. A lot of people, me included, are waiting for that.