File sharing uploads

[Ben M]

Hey crew

I do a fair amount of file uploads to either Dropbox or Hightail.
Lately I've noticed if I upload the same file to both file sharing sites they read the files as different sizes.

Eg. I'm uploading a 156Mb file to hightail now but if I place the same file into Dropbox it see's it as a 152.74 Mb file.

Does anyone have an explanation why?

Thanks in advance.

[Drumstruck]

Dropbox compression algorhythm?

[Ben M]

right...well.... that ends my use of dropbox.
3-4 Mb difference is nasty.

[Paul Maybury]

Dropbox uses a compression algorithm?

[lonearranger]

Ben,

Think you will find its the difference in how 1meg is calculated. Some people take it as 1million bytes, whereas others will use a binary MB which is 1024 x 1000. There is also a convention of using 1024 x 1024 as a MB. In windows a file will show as 43.8Mb (45936724bytes) when you view properties, and in explorer is appears as 44,861Kb.

Pretty sure this is the case with what you are seeing in dropbox. If you download your file from dropbox, via browser to different location, does it show as the same size? If you run diff(on osx shell) or FC/b (windows/cmd) this will do a byte by byte comparison.

If dropbox were destructively compressing files there would be masses of issues, especially with binary files like zip files which contain checksums to ensure they stay intact.

Applying this to your 156MB/152.74MB example file I would suggest your original file size is 156.4Mb.

We use dropbox extensively for graphics and audio with no issues.

Cheers

[Ben M]

Thank you Michael.
That 156.41 Mb was spot on.
Thanks for the explanation.

[Chris H]

Also,you can do a null test to check if uploading to Drop Box is causing any change to your original file. Always handy for peace of mind.

[Kurt]

If you are concerned about file integrity, zip wav files before uploading them. As mentioned earlier, zip files contain information to ensure they are perfect, wav files don't.

Or, get a freeware checksum calculator and upload the file with it's checksum, that way it can be tested when downloaded to ensure it is a perfect copy.