A word processor like MS Word or LibreOffice Writer will probably refuse to open it, giving some error such as “unsupported file type.”
Depending on how much of a nerd you are, the plaintext editor your OS comes with may either also refuse to open it, or open it as if it were plaintext and you might see a few jumbles of letters and punctuation, or weird symbols if it interprets it as unicode. According to Vim, my mp3 copy of Glycerine by Bush is mostly @ symbols. I noticed that my Bash shell didn’t want to autocomplete “Vim glycerine.mp3” but when typed manually it did it with minimal fuss.
If you open it in a hex editor, you might be surprised to see the first few lines are readable, they likely contain metadata that media player software like VLC can understand, like the track name, artist, year of release and such. Scroll down further and you’ll start to see more gibberish where it’s trying to interpret the individual bytes that make up the audio as ASCII characters. Funnily enough hexedit gave me a different looking bunch of gibberish than Vim did.
Only one way to find out
All files are made up of “text”, or rather, numbers. How each program interprets those numbers differs depending on the kind of work they do. Any program can open any file, but the way it translates those numbers won’t make any sense if the file wasn’t intended to be opened by that kind of program. So, if you opened an MP4, you might see a little bit of metadata that was encoded in a way the text editor can understand, and then you’d get a ton of random symbols, some that are numbers and letters you recognize, but a lot of them would be specialized characters from farther on in the list of characters whatever font is being used might have.
Think of it this way: take two human languages that use the same writing system, like German and French. Suppose you ask a Frenchman who also speaks English to translate and write down a few specific sentences. You then take those sentences to a German who also speaks English (but not French) and ask her to translate it into English. Obviously she can’t. She might be able to sound out the words, but neither of you will know what it means, and it probably wouldn’t sound right to a French speaker. Or better yet, you can ask her to try and guess what each word means. She’d likely come up with mostly nonsense (minus a few cognates and loanwords). This isn’t an exact analogy, but that’s basically what’s going on.
MS word and whatever Open/libre Office equivalent will likely throw a format error and show the encoded data as question marks inside a diamond.
Nothing horrible will happen, the MP3 will be fine the word processor will spaz out a bit.
It’ll likely crash the editor, but if it doesn’t then you get cool Matrix code. That’s actually how we used to make Matrix backgrounds back in the day, open an image in a text editor, copy the code, transform it to vertical, change it to green, eureka!
But what is all that crap? Is that the literal machine code or something? Like what is it and in the eff does it actually goid-enough approximate its subject content?
Every file is made up of zeroes and ones, what’s different between the formats is how those zeroes and ones are interpreted. When you open a mp4 in a text editor what you see is the result of the text editor interpreting the data as if it were text. Since the data doesn’t actually represent text, the result is meaningless garbage.
All any file is is just numbers. Opening a file in a program is just interpreting those numbers. To over-simplify, in a plain text file, for example, the number 32 means “space character”, and the number 10 means “move down to a new line”. In an audio file, the numbers are going to have meaning related to volume and frequency of sound, at points in time.
