Edit: Poor video performance on android using MX player

[beyondinferno]

I was having issues with mx not playing audio on mkv but have solved that by installing a codec pack. Now the issue I'm having is once video starts playing (takes a REALLY long time) and is using HW+ it gets really choppy playback. I'm using this on a droid DNA (snapdradon s4 pro) so the cpu power shouldn't be an issue. here is the transcoding string "ffmpeg -ss %o -i %s -async 1 -b %bk -s %wx%h -ar 44100 -ac 2 -v 0 -f flv -vcodec libx264 -preset ultrafast -threads 0 -"
Any ideas?

[beyondinferno]

Also, I should add my whole collection is mkv.
I can't find any documentation for the new feature so I'm having a hell of a time figuring this out.