[MX Player] br0adband:
MX Player Pro owner here (paid for it years ago and never regretted it for a single second), LG G Flex 2 (Snapdragon 810) and just testing out some x265 HEVC 10-bit clips at the moment, some Blu-ray encodes that show the following MediaInfo:

Video
ID : 1
Format : HEVC
Format/Info : High Efficiency Video Coding
Format profile : Main 10@L4@Main
Codec ID : V_MPEGH/ISO/HEVC
Duration : 1h 48mn
Bit rate : 1 998 Kbps
Width : 1 920 pixels
Height : 1 040 pixels
Display aspect ratio : 1.85:1
Frame rate mode : Constant
Frame rate : 23.976 (24000/1001) fps
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 10 bits
Bits/(Pixel*Frame) : 0.042
Stream size : 1.51 GiB (84%)

With default MX Player Pro settings I get very laggy and stuttered playback as expected so I changed from the default to 8 cores (since this is an octa-core device, 4 little/4 big cores) and also enabled the "speed tricks" which did improve things a bit but, after a minute of playback the audio and video just always end up out of sync on that clip. Will try others here shortly including some 8-bit x265 HEVC. Obviously x264 is not an issue at all considering, but I like many other people are going to move towards using x265 HEVC here (my process is underway hence this testing).

I suppose at some point I'll find a new smartphone with actual x265 HEVC hardware decoding support so this will become another non-issue but for the moment it is - but that's to be expected, right? :D

EDIT:

After seeing that link above to Qualcomm's 800 series SoC info page, and finding that the Snapdragon 810 I happen to have in this Flex 2 does have HEVC hardware decoding support, now the precise question becomes:

Which specific HEVC profile does the Snapdragon 810 support with respect to hardware decoding, and is it only going to work for 8-bit and not 10-bit encodes? I'll be testing an 8-bit encode here in a few minutes to see and watching the CPU usage as it happens. Obviously if the CPU usage drops to very low levels then I'll have that answer I suppose. I'm going to bet it's only got 8-bit x265 HEVC support which is fine with me really, I know everybody is all over 10-bit encoding but since I don't care about anime/cartoons/etc I really don't give a damn.

Yes I realize that 10-bit can be more efficient overall in terms of file sizes but if I end up using 4x the battery power to watch a clip that's a few hundred megabytes smaller believe me, I'll choose to play the larger clip with longer battery life without even thinking about it. :)

EDIT2:

So yes, it's just 8-bit x265 HEVC decoding support for the Snapdragon 810. I grabbed those "jellyfish" demo clips at 3/5/10/15/20/25/30/40/50 and even 60 Mbps and they play without issues with HW+ enabled. It's defaulting to starting playback in SW mode and of course lagging like a mofo when it does but switching it to HW+ then kicks in, CPU usage drops to almost nothing as the GPU acceleration goes into action so, now I know for sure.

I'm still going to do things with 10-bit x265 HEVC for the time being since it does offer better potential in the long run but the lack of hardware decoding is a bit of a minus. Guess I'll just have to deal with it for the time being as I start looking into a newer device for the future, perhaps the Flex 3 will have 10-bit HEVC decoding support, who knows but we'll find out soon enough.