Yes... but not quite. It will be able to decode up to a certain bit rate, after which it will fall apart. If you want to better understand what will happen, you can use test files from
this site.
I made a small test for you in case the CPU you have in mind is not in your possession - I used the 1080p 40Mbps Main 4.1 encoded file from the mentioned site on my Haswell machine, and tried to emulate the Celeron by restricting max frequency to 2.7Ghz and letting the media player use only 2 threads. Here's how CPU usage looked like:
The above screenshot is with hybrid decode disabled, software only decoding. The clip played almost ok, with only 1-4 dropped frames right at the start. Enabling hybrid decode or increasing CPU frequency a bit made the clip play without any dropped frames.
Now, in case you're wondering why would I not test with hybrid decoding always enabled, it's because things get complicated once you increase bitrate and also have a bit more CPU grunt available (4c/8t, dual channel RAM). In my case, using the 110Mbps file with partial HW acceleration resulted in bad quality playback (dropped frames), while going software only resulted in good playback. Just realized G1820 does not have any form of HW acceleration for HEVC anyway.
So quick recap:
- test on your own system with your own software - software and drivers will play a big part here
- my (very) limited testing says you should be able to play FHD files up to 40Mbps
If the Haswell Celeron is an upgrade option, I would suggest against it: either upgrade current HTPC with the cheapest HEVC Main10 video card available, or wait until Q1 2017 and buy a cheap Kaby Lake or whatever APU AMD brings about that can decode HEVC and VP9.
I forgot to mention that I already have a Haswell motherboard (LGA 1150) lying around, so my choices are limited...
Well, you can go with the Celeron for now, but soon enough you'll need to add a dGPU for proper support.