[LG Optimus 2x] spawndk:
Lets clear up a few things here

support for the mkv containter are fully supported by the native LG mediaplayer in the latest firmware (v10c/d), but not in the previous firmwares.

If one has the latest firmware, then nothing needs to be done to enable mkv playback.

If the native LG mediaplayer do not show mkv files in the media list at all, then one does not have the latest firmware !

If the native LG mediaplayer do show the mkv files in the media list, but complain when trying to play the files, then the mkv files contain some video or audio format which is not supported. For instance are DTS audio not supported, thus trying to play an mkv with a DTS audio track will not work. Propably AC3/DD are not supported either, or flac. An mkv can also contain a non supported videoformat. In other words, if the files do not show then its wrong firmware, if they do show but dont play, then its not because mkv are not supported but because some video or audiotrack inside the mkv are not supported.

support for mkv are not a codec question, since mkv are just a container and not a video format. Codecs are used to decode video (and audio) formats. Parsing containers like mkv are just a matter of having a parsing filter and support for the extension .mkv in the media build properties. Codecs are used to decode the video and audio formats inside the container after the parsing filter has parsed the container and send the video and audioformats to the decoders.

The typical videoformat inside mkv are h264/mpeg-4 (but can be many other formats also), this format has allways been supported on all firmwares but only inside mp4 containers up untill the latest firmware, the only thing new in the latest firmware in this regard, are the addition of a parsing filter for the mkv container.

For best playback of mkv (and the h264 video inside) only the native mediaplayer should be used, because the hardware acceleration from the Tegra chip is needed and most third party media players do not have full access to this hardware acceleration Instead they use software decoders which are not as effective. A few third party media players do have hardware acceleration, but they dont offer any better playback than the default LG mediaplayer because when hardware acceleration is used then it makes no difference which media player interface is used to call it. The playback quality will be identical, therefore there are no point in using third party mediaplayers except for playing other types of videofiles which the native mediaplayer do not support at all, but may be supported by the software decoders in the third party player. But for supported files the default LG player will play as good or better as third party players.

If playback of an mkv containing a typical h264/mpeg-4 videotrack plays poorly, with video distortion/pixelation or other problems, then its because the video has been encoded with to high encoding levels. Most pirated 720p/1080p rips in mkv that people download from the internet are encoded using higher encoding levels than what is supported by the Tegra chip - typically they are encoded in profile level High@L4.1 and the Tegra chip only support up to Baseline@L4.0 for 1080p and possibly Main@3.1 for 720p

If playback are poor because of to high encoding profiles have been used, or the mkv contain some non supported video/audiotrack, then the only sollution are a reencoding of video and/or audiotrack to a supported format using a supported encoding profile setting.

read more on h264 and encoding profiles here:

http://en.wikipedia.org/wiki/H.264/MPEG-4_AVC

and use media info to get information about your mkv files regarding video and audio formats inside, and which encoding profile has been used to encode video with

http://mediainfo.sourceforge.net/