1. What program is used for hard subbing anime videos?
2. About .mkv...why is it so popular? It lags like every 5 seconds in some videos and takes longer to skip from one part to another. Plus the subtitle seems to be unable to show 2 or more lines at once(like when people talk at once)

If you are having probs playing things in the mkv container try vlc player - itsd free and plays anyithng.

If you are having the prob when editing mkv files - that is normal, inside is often hoghly compressed dvix/xvid video and this is always a bitch to edit.

As for adding subtiltels - any decent video editor will allow you to do this by adding a text track.

Thank you sir for the quick answer.
I'm using gom player and it plays mkv files fine. It's just that some mkv videos lag very badly and the sub is almost always messed up. I still don't understand why .mkv is popular. If the merit is the soft sub, isn't there a way to soft sub .avi files as well?