Base64 decode gives garbled result - base64

I copy and paste a text from the web that is base64 encoded to this site http://www.motobit.com/util/base64-decoder-encoder.asp ,
but it gives a strange result , it look like a garbled.
May i ask ....how can i decode the text correctly , thank you.
nUł"˘ÂUÓ"…F˙i+Şž›‘Ş˘éăŁqëKĄ®qâ %˘ dŞn‘ĄŐňŢ^{łcąWq\)ńÂÔ€
Here is the base64 encoded text
blWzIh+iwgYbVdODDyKFRv9pFCuqnpuRqqLp46Nx60ulrnHioCWiIARk-qm6RpdUB8t5ee7NjG7lXcVwp8cLUg==

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Convert HTML to base64 in nodejs with special characters

I have created an api to convert html file to base64 string like this
let base64File = new Buffer.from(req.file.path, 'utf8').toString('base64');
It works normally with simple html file , but when it comes to html file with special characters example like : "«", "Â",... it changed to � when i write back to html. I noticed that i tried using online tool like https://codebeautify.org , it returns different result from mine (but the result proviedd by it write back to html normally) but same result for simple html file.How can i convert correctly?

Base64 Decoding results contain unknown characters

I have base64 encoded text and I try to decode it but when I decode it, it contains some unknown characters. But the interesting part is, decoded text contains that I need data. So just I need to remove unknown characters and I need to split the data.
Do you have any suggestion to escape this unknown characters?
E.g base64 data:
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
It is a base64 encoded protobuf data. you can decode it from https://protogen.marcgravell.com

issue decoding base64 text: prefix "77u_" causes junk output

I'm currently trying to decode my base64 encoded string. The issue I'm facing is it gives me junk decoded result but when I remove 77u_ in front from it, the decode result will get fine. My question is that, is there any other way to decode it?
Following is my encoded string:
77u_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
It's the _ that messes up the result. Everything else is perfectly fine base64 encoded. The base64 code table doesn't contain a _, it is a substitiution character for / in base64url encoding.
When you replace _ with / the decoding works fine.
When I tested it on https://www.base64decode.org/ and chose ASCII as the source character set, I got  in front of the text, which is the byte order mark for UTF-8. When I changed to utf-8, there was nothing visible in front of the text.
A short test in node.js also proves that '77u/' is indeed the base64 code of the BOM:
var messageB64 ='77u/'
var buf = Buffer.from(messageB64, 'base64');
console.log(buf) // output: <Buffer ef bb bf>
Conclusion:
your data is base64url decoded
you should change it back to base64 code before you decode
the extra characters are a harmless byte order marker which is invisible if you use utf-8 encoding.

I have encoded string but i don't know what type is it

I have two encoded strings that used same encoding method but i don't know what type it is.
I have tried using base64 decode but it didn't work.
This is the first encoded string I have 3qpY0Vw86MZykGfqc7jnVg==
This is the second encoded string I have nB6dtl3iA5IE1Z+g9SpBrw==
They are using same encoding method.
I want to know what type of encoding that used in that strings. Also I want to know how to decode it.
Those base64 payload may be containing something else than a string, like a raw binary, an image, a ciphered payload, etc. that can't be displayed as text.
base64 is not exclusively used to encode text.
For example to save to a file:
$ printf %s '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' | base64 -d > stackoverflow.png

Disociate an image and text from a base64 encoded string

I'm coding an API in ASP.NET that receives base64 encoded string to parse them into a DB. My problem is the following : these strings contain both an image and some text following it and I cannot find a way to separate them to then process he text part. Of course I have no possibility of changing the format.. So I was wondering if someone had an idea or a tool to detect the begining and end of the image and the text parts?
Here is a sample :
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I cannot comment, so I post this as an answer:
You could decode the base64 encoded string to binary and try to detect the magic number of the image (assuming it has one). if it is an JPEG image it has a start and end signature. a BMP has the size of the image encoded into the header.

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