I know they're both container formats and what matters is the actual codec used, but what I don't know is if video converting software will do anything to change the codec, or if it just repackages.
The reason I need to know is that I have several .avi files with subtitle files, and I'm wanting to turn them into .mkv so I can attach the subs and not need a second subtitle file anymore. Will my new .mkv files be identical in video and audio quality to the original .avi?