Compression for size reduction

Posted on 2007-08-07
Last Modified: 2013-12-01
I have some quicktime videos that include some data files a couple of images etc. There may be five main folders within each archive.  So each archive may be 5Gb.  I don't know what output size I am looking for ( i am not sure what's possible) but half would be nice.  I am using winrar but open to suggestions...thanks
Question by:chadaort
    LVL 22

    Expert Comment

    I don't think you will be able to reach that goal. For the most part I have not seen much difference in compression programs as far as amount of compression goes. Also those types of files typically just will not compress very much.
    LVL 63

    Expert Comment

    I agree. They are already compressed.

    Maybe there is some specialized programs for this, but I have not heard of anything offhand.

    LVL 25

    Accepted Solution

    As mentioned compression of video is pretty limited with things like rar or zip.  Probably less than 5%.  The data files might do better if they contain uncompressed data or are a format that is not very dense like text files but I am guessing the video is probably a much larger portion of the files to be comrpessed.

    To significantly compress the video you will need to re-encode using a different codec or a different format.  A program like Quicktime Pro will allow you to do this.  Of course this is only going to work if the current format is not allready optimized for size.

    Also a open source freeware converter which can handle most any format going,

    Author Comment

    Now this was my thoughts on compression up till this point.  I got a rar file from a cousin with some tutorials on it.  The size of the archive was 185,222 KB and after extracting it put out another rar file and the size was 801,164 KB.  The I extracted that file to reveal three tutorials each in its own folder.  The size of the folders are 293 MB, 114 MB, 374 MB.  Now is there a way to tell how the compression was done?  I went to properties and the archive tab but didn't seem to see anything helpful there.  

    Author Comment

    Ok the original is a .rar (185,222) file but it extracts an .iso (801,164).  Does .iso get that much better compression?
    LVL 25

    Assisted Solution

    The iso file is a disk image file not a compression format.  If you add up the sizes of those folders they are smaller than the actual iso file size.  This is not uncommon due to differences in the formating used on hard drives vs optical media.

    So the only compression going on is the rar.  Data compression is sort of universal in that something can only be compressed so far.  So applying compression more than once typically makes little to no difference.

    Audio and video compression is a bit different than data.  With data it needs to be able to be uncompressed to be exactly the same as when it was compressed.  Video and audio compression does not need to be so strict.  So formats like jpg, mpeg, mp3 etc can be used to shrink video and audio files at the expense of the quailty of the picture and/or sound.  One drawback it that  once this has been done you can never recover the orginal's quality.  This is called 'lossy' compression.  

    Ultimately you can give it a go with rar and see what you get.  It may be that the files are not that dense to start with and you could get decent results.  It's not impossible,  just less likely with multimedia formats as most have allready got some degree of compression to start with.    It certainly does not hurt to try.  If you do not get the results you want then you can look into re-encoding your multimedia files into a more compact format.

    Rar provides decent compression so even though there are a number of other general purpose formats the results are not going to be that much different.  If you have something that needed to be just slightly smaller it might be worth trying other formats to shave a touch off.

    Of course using something 'non-standard' can be annoying as people may not have the tools to uncompress your files.  Zip is not the best,  but chances are anybody will have no problem opening it.


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