I am not well acquainted with the forum's best way to report that kind of thing, so please excuse me if i am not doing it properly.
HTC dispatched earlier this week an update in my region for the stock HTC One M8 (europe).
I do not know what it was before, but now it is under android 4.4.3 and Sense 6.0 (2.22.401.5, kernel 3.4.0-ge224610)
I am using MX Player Pro 1.7.31 (activated, of course), and i don't believe it has updated at the same time as the HTC one.
Before the update, H/W+ and H/W was working very fine with my collection of videos (of various container types and encodings), be it high bitrate full HD 24fps (for broadcast ballet) or low bit rate more "standard" resolutions. It had a "hold" (were a frame is kept too much, creating a choppiness) every now and then (less than one per couple of minutes) but it was very subtle and not intrusive.
After the update, H/W+ and H/W are unusable for ballet, the hold is very noticeable and much more frequent (up to every other second sometimes), in fact it sometimes looks like the framerate is globally reduced as well, independently of framerate and resolution, every video has the fluidity issue even the ones that were playing flawlessly on my old legend.
My playback conditions are in the same conditions always, i use airplane mode, and it has been observed on the course of several days, with various uptimes (same after a fresh long OFF-ON or a 1 day uptime).
The system load oscillates between 8 and 20% before starting mxplayer (with the monitor using a good share of it )
S/W is much smoother, without hiccups.
Log files show no error message during playback... it is just choppy. Just for info i attached a report (i didn't play long runs this time around).
So, fellow HTC users, if it is not limited to my very phone (i'd be surprised), it's time to move on to S/W decoding for the time being, works very well with the platform... I hope it won't tax too much the battery when i am in a train.