Changing File Extensions (clarification please)

[mesakid]

I remember before that it was possible to change the extension of a file, just by it's file name, and the file itself would change to a specific file that I issued it as...but for some reason, my computer is not capable of doing that.

For instance

run.mpg would be a movie file

but if I changed the extension to

run.txt

it would still be in the format of mpeg. but the extension txt would still be there. and my computer recognizes it as mpg.

actually, it would appear also like

run.txt.mpg---a double extension

I am positive that I was able to change the extension of a file, and the file itself would change it's format, but not entirely (like avi-to mpeg) that's not what I mean, I just mean, changing the extension, changes the program it opens up with (without manually opening it)

What I'm trying to get at, is changing some files into a txt file, where I can upload the files much quicker and easier, as text files dl and upload much faster on 56k, but after dl, be able to change it into the original file format extension, to be able to function.

So,asking for help on this thing, if it isn't possible, than I must have hallucinated a while back, but I'm for sure it's possible.

[mairving]

You can change the file extension if you want but it's not going to make it a text file and the file is going to be the same size. You could try compressing it using Winzip or Winrar but mpg are already compressed and won't compress much further.

[doctorgonzo]

Giving a large file a .TXT extension isn't going to magically make it smaller, nor will it make it faster to transfer over a dialup connection. As mairving said, only compressing it using a compressing utility like WinZip or WinRAR will actually make the file smaller.

The file extension is just a part of the file name. Sure, Windows uses the extension to try to figure out what kind of file it is, but keep in mind that there is absolutely NO hard-and-fast connection between file type and extension. A .MPG file with a .TXT extension is still an MPEG file. The only difference is that Windows will attempt to open it using Notepad or some other inappropriate utility. Put another way, the extension is not guaranteed to contain any metadata about the file itself.

[glc]

If you want to change the extension (disregarding whether it will open in anything) you need to go into your folder options and uncheck "hide file extensions for known types" - then you can rename all you want.