It can house multiple audio tracks (e.g., different languages) and subtitle tracks (e.g., SRT or SSA) within one file.
Digital copies of these movies shared online often use the .mkv extension due to its ability to support high-quality video and multiple subtitle tracks. 2. Software & Technical References
Without more context, it's challenging to provide a more specific interpretation. If you have more details about where you encountered "143 mkv" or what you know about the file's contents, I could offer a more targeted explanation. Are you looking for information on how to play these files, what they might contain, or something else?