SGS2 Exynos plays MKV HP@L4.0 1080p as a matter of fact.
Stock KE2 no overclock, rooted.

The sample I have of Inception plays perfectly:
Code:
~/Torrents/Inception.2010.1080p.BluRay.DTS.x264-CtrlHD $ mkvinfo sample.mkv 
+ EBML head
|+ EBML version: 1
|+ EBML read version: 1
|+ EBML maximum ID length: 4
|+ EBML maximum size length: 8
|+ Doc type: matroska
|+ Doc type version: 2
|+ Doc type read version: 2
+ Segment, size 90069522
|+ Seek head (subentries will be skipped)
|+ EbmlVoid (size: 4044)
|+ Segment information
| + Timecode scale: 1000000
| + Muxing application: libebml v1.0.0 + libmatroska v1.0.0
| + Writing application: mkvmerge v4.4.0 ('Die Wiederkehr') built on Oct 31 2010 21:52:48
| + Duration: 61.604s (00:01:01.604)
| + Date: Mon Nov 22 20:44:54 2010 UTC
| + Segment UID: 0xbc 0xee 0x26 0x58 0x42 0x96 0x31 0x6b 0xb9 0x0c 0x7b 0x5f 0x16 0x6d 0xc2 0x59
|+ Segment tracks
| + A track
|  + Track number: 1
|  + Track UID: 1
|  + Track type: video
|  + Lacing flag: 0
|  + MinCache: 1
|  + Codec ID: V_MPEG4/ISO/AVC
|  + CodecPrivate, length 40 (h.264 profile: High @L4.0)
|  + Default duration: 41.708ms (23.976 fps for a video track)
|  + Video track
|   + Pixel width: 1920
|   + Pixel height: 800
|   + Display width: 1920
|   + Display height: 800
|  + Content encodings
|   + Content encoding
|    + Content compression
|     + Algorithm: 3 (header removal)
|     + Settings: length 1, data:  0x00
| + A track
|  + Track number: 2
|  + Track UID: 2917809285
|  + Track type: audio
|  + Codec ID: A_DTS
|  + Audio track
|   + Sampling frequency: 48000
|   + Channels: 6
|  + Content encodings
|   + Content encoding
|    + Content compression
|     + Algorithm: 3 (header removal)
|     + Settings: length 4, data:  0x7f 0xfe 0x80 0x01
|+ EbmlVoid (size: 1123)
|+ Cluster

It also plays Youtube 1080p from the desktop site. The browser seems to be hardware accelerated because it is smooth as hell! I kid you not.
Samsung Galaxy S4 I9505

CyanogenMod Release Notifier: Python 2.7
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