what is the reason for same files having different MD5

K

kenny1999

Member
I've got two files they are virtually the same - but they are from different source and were downloaded by different method , one was by IDM and the other was by JDownloader. They are video files featuring the same thing, they have same length of playing time, same resolution and those frame bits rate are same as well, all the same, but when I compared their MD5 they are different

and I looked at the file under windows properties, one gets a size "313,829,873 bytes" and the other has a size "313,829,876", which is only 3 bytes different

Now my question is, is that one of the video file got damaged in quality? what cause the 3 bytes little different?
 
well basically to explain the MD5 Sum is that its an encryption to check the file and see if it actually is a file, best way for me to explain it really.. If somepart of the video the image has a frame lag spike then that will have to change in the MD5 sum. Also a file might be an exact copy of something but it still is different, as 2 files (that are the same) cant have the same MD5 checksum.
 
The same file can have the same sum, period. If you are missing one byte, or in your case just three, the sum will be drastically different however.
It's common to get a bad download no matter how you do it. Connections can get dropped, etc. In most cases, it's normally of no significance, as is the case for you. Other times however, It can render whatever you download as trash since it won't run as intended, or run at all.

Raz3rD said:
Also a file might be an exact copy of something but it still is different, as 2 files (that are the same) cant have the same MD5 checksum.
Click to expand...
Erm, if that was the case what would be the point of having them? The whole point of them is to verify the file is complete and unchanged, down to the last byte. So yes, you CAN have the same checksum.

To illustrate the point further, I made a file named a, copied it to b, then checked their sums and their contents. They are the same

Code: 
nyxcharon@Guinness ~ $ echo "test" > a
nyxcharon@Guinness ~ $ cp a b
nyxcharon@Guinness ~ $ md5sum a
d8e8fca2dc0f896fd7cb4cb0031ba249  a
nyxcharon@Guinness ~ $ md5sum b
d8e8fca2dc0f896fd7cb4cb0031ba249  b
nyxcharon@Guinness ~ $ cat a
test
nyxcharon@Guinness ~ $ cat b
test
 
Last edited:
NyxCharon said:
The same file can have the same sum, period. If you are missing one byte, or in your case just three, the sum will be drastically different however.
It's common to get a bad download no matter how you do it. Connections can get dropped, etc. In most cases, it's normally of no significance, as is the case for you. Other times however, It can render whatever you download as trash since it won't run as intended, or run at all.


Erm, if that was the case what would be the point of having them? The whole point of them is to verify the file is complete and unchanged, down to the last byte. So yes, you CAN have the same checksum.

To illustrate the point further, I made a file named a, copied it to b, then checked their sums and their contents. They are the same

Code: 
nyxcharon@Guinness ~ $ echo "test" > a
nyxcharon@Guinness ~ $ cp a b
nyxcharon@Guinness ~ $ md5sum a
d8e8fca2dc0f896fd7cb4cb0031ba249  a
nyxcharon@Guinness ~ $ md5sum b
d8e8fca2dc0f896fd7cb4cb0031ba249  b
nyxcharon@Guinness ~ $ cat a
test
nyxcharon@Guinness ~ $ cat b
test
Click to expand...


How to avoid bad download? In other words, how to ensure the downloaded files are exactly the same perfect copy from the server one?
 
You must log in or register to reply here.
Back
Top