Compressing files

Discussion in 'macOS' started by csmitty, Feb 9, 2009.

  1. csmitty macrumors regular

    Joined:
    Sep 15, 2007
    #1
    So I tried out apples built in compress feature and it took my 1.7gb file down to a whole 1.67gb. Thanks. Is there a place where I can go to change the compression ratio or whatnot?
     
  2. Tallest Skil macrumors P6

    Tallest Skil

    Joined:
    Aug 13, 2006
    Location:
    1 Geostationary Tower Plaza
    #2
    What are you expecting? 500MB?

    Some files can't be compressed very much because of the nature of their contents.
     
  3. Makosuke macrumors 603

    Joined:
    Aug 15, 2001
    Location:
    The Cool Part of CA, USA
    #3
    It's standard zip compression, which is the same as that built into XP and dozens of other tools.

    What were you compressing? If it was video, no lossless compression format in existence will make much difference (if it would, the video compressor would already be doing that, after all). Photos, similar. If it's a folder full of text files, you should get a lot better ratio than that, but again, it's just standard zip compression--does what it does.

    You can always try downloading Stuffit and see if it does better with your files--the newest version uses a relatively advanced scheme.
     
  4. Heb1228 macrumors 68020

    Heb1228

    Joined:
    Feb 3, 2004
    Location:
    Virginia Beach, VA
    #4
    Already compressed files (.mp3, .aac, mpeg-4 video files, etc...) don't have much room left for compression. You can get apps that will work harder on compressing, but will take longer to compress and reopen. You may get 5 or 10% difference in file size for twice as long waiting for the file.

    Disk space is too easy to come by for file compression to be a very big issue anymore. Here's something I found with a Versiontracker search:

    7zX - 1.7.1 file archiver with high compression ratio
    http://www.versiontracker.com/dyn/moreinfo/macosx/29005
     
  5. csmitty thread starter macrumors regular

    Joined:
    Sep 15, 2007
    #5
    I always figured it would compress to whatever % of the original you told it. I've compressed many large pictures and drawings at work on xp with just winzip and it will compress to 90 something % of original. This is the first time i tried it with video and was expecting alittle more than 300MB. Its a 848x480 60min mpg video. Guess I shoulda shrunk the res further. But damn if my macbook doesn't hate doing it.

    Thanks for the replies.
     
  6. sidewinder macrumors 68020

    sidewinder

    Joined:
    Dec 10, 2008
    Location:
    Northern California
    #6
    You really need to read up on how compression works.

    The compression you are talking about using WinZip is called "lossless" compression. With lossless compression, the source file and the compressed file would contain the same exact data if it was uncompressed. You don't just pick a compression level. The data being compressed might not compress at all if the data in the file is already highly compressed.

    Another type of compression is "lossy" compression. With lossy compression there is a loss of data.

    Lossy compression is fine for music or image files, at least to a certain degree. But you would not want to use lossy compression on text files, documents, or spreadsheets.

    Anyway, if a file compressed X percent on a PC, there in no reason to think it would not compress as well on a Mac. It all depends on the software used to do the compression.

    S-
     
  7. mlts22 macrumors 6502a

    Joined:
    Oct 28, 2008
    #7
    There are a number of compression utilities on a Mac. If you are wanting to dip your toe into the command line waters, you can use tar and bzip2 which gives as good compression as you are going to get unless you use a utility that uses special compression technology for each file type.

    If you want the best compression you can get on any platform, I'd highly recommend picking up a copy of Stuffit Deluxe from Smith Micro. This has been a one of the de facto Mac standards well... since 1987 pretty much. Stuffit Deluxe is able to repack already compressed files like JPEG files resulting in a file that has the same data quality, but a smaller size.

    I use it because it allows one to add some error correction to archives, so if an archive gets a bit or two flipped or a header chewed off, all the data is completely recoverable.
     
  8. Makosuke macrumors 603

    Joined:
    Aug 15, 2001
    Location:
    The Cool Part of CA, USA
    #8
    Those were likely large, lossless images in PSD, BMP, or TIFF format; unless you enable compression in TIFF (which is if memory serves basically just the zip routine) they're tremendously inefficient, and so file compressors will drastically reduce their size.

    Either that or you were recompressing an image as JPEG, which as explained above is lossy, and so you can compress it as much as you want--the visual quality just goes down.

    You were starting with an MPEG video file, which by definition has already been run through a relatively efficient lossy compression scheme. So lossless compression--zip in this case--will do almost nothing to them. Recompressing (usually called "reencoding") the video at either lower res, lower quality, or with a better video codec (if it's MPEG1 video, try H.264 in an MPEG4 container), or all of the above to get it to the size you want.

    Most video encoders will let you just pick a desired bitrate, so you decide on what filesize you want and the quality follows from your bitrate limit.
     

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