John. My limited understanding is that checksum is purely a binary comparison of the files. The first question is asks is if both files have the same number of bits. Then it breaks the file into pieces, adds the value of the bits in each section (0 or 1), then compares the results. If the files are the same size and the sums of each section are within a preset tolerance, the files are considered the same. The process can be really helpful in audio/video where a replaced shot or section of dialogue may not change the file size or structure. Other than the timestamp and hopefully the file name, both files may look identical. Checksum should notice that they are different from each other. JB
On Feb 12, 2023, at 8:23 PM, John Moore <bigfish@pacbell.net> wrote:
I got 4 files through drop box. Three with the same title on one day and the next day another file. They were all separate drop box downloads. The first three had the exact same title and the last one has a similar but incremented title ending in 02 instead of the first three that ended in 01. They all have the same content and have the same metadata when checked in Media Info program. The first three that came in one day I updated the file name including download 01, 02 and 03. I ama linked to the 01 file but when I then go to ama link to the 02 and or 03 file it appears in the bin with the 01 clip name like the first one. Even if I link in a separate bin it still takes on the 01 ending clip name. This also happens when I ama link to the file sent the next day that actually came with the 02 on the end. This made me think all the files are identical so I did an md5 check sum and they all generate the same character string so that means they are identical.
My curiosity is why doesn't me renaming a file make a change in the md5 checksum? It makes me think that the md5 doesn't look at every aspect of the file but just at the "meat" of the file. I don't know if that would be considered the video essence or what? If it verity's a that two files match and are identical why doesn't changing a files name effect the md5 checksum? I can see the value in the name not counting in the equation but I'm just wondering what aspects of a file are involved in the md5 and what aren't. Just a curiosity that came out of this experience.
John Moore Barking Trout Productions Studio City, CA bigfish@pacbell.net
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