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I have some home videos on my dropbox as mp4s, I wanted to download them again. I found the speed to be about 20KB/sec. However I noticed that if I renamed the file extension from mp4 to something else like dmg then it downloads much faster (like 200-500 KB/sec).

Is there something that can slow down files that appear to be videos. Renaming the file's extension doesn't affect the 1s and 0s, so it seems renaming should have no affect on the speed?

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Maybe dropbox is delivering media-date slower to prevent streaming. –  fragmentedreality Jan 9 '13 at 14:56
    
it works with other sites as well. –  Jonathan. Jan 9 '13 at 14:59
    
By "it works" do you mean that .mp4-downloads are slowed down on other sites, too? –  fragmentedreality Jan 10 '13 at 10:13
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3 Answers

That can only be one ISP-side or if you are behind a "communist firewall". If your internet isn't being censored, there should be no difference on speeds based on extensions.

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Regardless of the file extension, the bytes remain the same.

It may be possible that some server side code limits downloads of certain types to protect/evenly distribute bandwidth use (to stop streaming media like video or music, for example), but as for what and why, well that is another topic I think and one which we can't conclusively answer as we don't know their rules!

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As others have pointed out two files of the same size should download at the same speed regardless of extension (everything else being equal).

Several things could be happening here:

  1. The source site is limiting the bandwidth available to each person downloading the file. Less likely if you say the problem occurs on other sites too.
  2. Your ISP is shaping your connection and throttling the speed with which you can download certain files.
  3. Your anti-virus software is checking these files differently to others causing the rate at which you can pull the files to be reduced.

I'd say the most likely candidate is 2.

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