Ware9 Free H.263 to MKV Fast, as its name, is free and can be used to convert H.263 to MKV. It is a good program for you if you want to convert H.263 to MKV accidently. It can convert at superfast speed and the converting result is relatively good. The interface is really simple, so it's easy-to-use. You can master it even without any help. It is a professional H.263 to MKV converter. Just try it.