Can someone please tell me the easiest way to have selectable subtitles in the MKV file when the video is encoded with XviD and the audio with AAC.

Thanks

IMO the easiest way is to use the mmg.exe GUI which comes bundled with mkvtoolnix package. It allows you to embed any number video/audio/subtitle tracks into the MKV file. However, you still need player support to display the subtitles properly.

Yes, in order to get your subs into mkv you must chose one of two methods or even both if you so desire. There are two different ways of putting "soft" subs in mkv these are text and picture subs. You can also put "hard" subs where the subs are overlayed onto the video and encoded with the video (not an ideal option IMO). Text subs can be done by OCRing the picture subs, yes this is a boring and tedious task and usually very error prone (if you are like me). You can use Subrip to do this. You can also extract the picture subs from your dvd by using VSRip; just open the ifo and press extract and it will do the rest. Then open mmg like niktheblak said and open the .idx file that VSFilter outputs if you are using picture subs. Picture subs can be compressed in matroska so they don't take up so much room with zlib IIRC. To playback use VSFilter which can play as well as switch subs. All the programs and filters you need are here http://sourceforge.net/projects/guliverkli/ cheers .

Thanks

I downloaded VSRip bit for some reason it does not produce a .idx file. It just creates a 1k .chunk file.

Why isnt it working?

You should use VobSub to open the .ifo and convert the bitmap subtitle stream embedded in the .vob file to .sub & .idx, which you then mux & compress into mkv using mmg as already explained.

Maybe you should try DVD Decrypter in IFO mode + stream processing (video and audio should be demuxed, subtitles direct stream copied) instead of vStrip.

I prefer using SubRip to OCR the subtitles. Contrary to Bonzi's experience, I find the process goes fairly quickly and is quite reliable. After the SubRip process, you only have a 50-100k textfile to deal with. There are some other advantages to using text-based subtitles, besides the slightly smaller filesize. For one, you can resize the text or change the font as you please, which you can't do without OCR-ing the subtitles. For another, you can render the subtitles in a high-resolution, anti-aliased font, which looks much better than the bitmapped font that a non-OCR subtitle ripper gives you. Finally, if you're so inclined, you can make your own additions or changes to the subtitles.

Another reason why I use SubRip is because I always seem to have trouble remembering how to work VobSub.

Yes this is strange. I had the same problem about a week ago and I could never convert them to vobsub. Sorry, I'm not more help about this but I never did figure out what was wrong .

how to zlib something on win?

mkvmerge uses zlib and will compress the subs itself for you as well as mux it into mkv.
EDIT: This is what you wanted to know right?

yup, tnx Bonzi.