*sigh* this whole thread is one whole misconception about containers. Blu-ray supports mt2s containers with MPEG2 and MPEG4 part 10 (h.264) video streams and with AC3 and DTS audio streams (including their "hd" versions. Blu-ray players DO NOT support MKV or mp4 files unless specifically mentioned e.g. PS3 MKV supports AC3, mp4 does not. MKV is more common because HDTV is mostly broadcast in AC3. Mp4 supports AAC and is mostly used when support for 3rd party device support is wanted e.g. mobile phones and Xbox360.