Why does renaming file extensions work?

[BluSky]

Hi all

I have a large number of dvds which I ripped to MKV files using handbrake. My question is why do they still work when I change the file extension to m4v, mp4, avi etc? It doesn't make sense to me because, as I understand it, changing the file extension doesn't change the file itself, just the way the computer decodes it...

All of the mkv's were ripped with h.264 and ac3 passthru.

Thanks for any help

 

[BluSky]

Hi, Thanks for the explanations. On a related note why is the audio much louder if I change the extension to anything other than MKV?

Thanks again