Can I compress a RAR file again to reduce its size?

Question

I had a 326 MB iso file that I compressed using WinRAR, with the best compression method. It got compressed to 144 MB.

I want to compress more and want it to be limited to something around 22 MB.

Is there a way I can compress the RAR file again? If not, is there any other way out?

Answer 1

If you've already compressed with best compression method, you can't compress further.. Few KB/MB could be digestible, but compressing 144MB compressed data to 22MB: No way!
I'd not say, its impossible. But.. Currently, there's no standard compression algorithm to do this. Sorry!

If 22MB is a limit somewhere (like cloud, storage), you can always use file splitters to split this 144MB file into multiple 22MB chunks. File Joiners (often, built-in with file splitters) reverse this process.

Answer 2

Is there a way I can compress the RAR file again?

Again? No, see this question for why a compressed file cannot be compressed further. If anything, re-compressing an already compressed file may even increase the resulting file.

If not, is there any other way out?

Your best bet is to either tweak the WinRAR settings to the file you were trying to compressing, or to use a better compression algorithm. 7-Zip supports several different powerful algorithms, and by tuning them just right, you could potentially get a big increase in savings over RAR.

I usually like to keep everything set to the maximum (figure 1). It takes longer to compress, but it’s usually worth it.

You can also try nanozip. It is an experimental archiver (read alpha) and runs very slowly, but gives shockingly good compression most of the time.

Of course, as always, compression results will depend on your file(s). You said you are compressing an ISO which is essentially just the contents of the files with little file-system overhead. Depending on the nature of the files, you may get some decent compression, but if it is an installation disk, then the contents of the main software are likely already compressed, so you won’t get that much more from the remaining files.

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Figure 1: 7-Zip settings set to maximum compression

Answer 3

Well, I'd prefer using the best possible method for compression cause I've tried recompression of a file that I've compressed lightly. My file didn't changed it's size.

But when I've decompressed it and then recompressed it using the best method, then I came out with flying colors

So plz do the heaviest compression

Answer 4

If you have a PC with RAM higher than 3 GB and processor about 3 GHz, use KGB Archiver.

At maximum compression and PAQ6 algorithm you’ll be able to reduce a file's size to a fourth or fifth of the original – but it's a very slow process.

Answer 5

It might make a little more sense to look at why you can't compress it further. In an oversimplified statement, compression would work like this:

Document Pre-Compression (110 Characters):

this is a document that has not been compressed. After this document is compressed the length will be shorter. 

Same document, Post Compression (103 Characters):

1:this
2:document
3:compressed
1 is a 2 that has not been 3. After 1 2 is 3 the length will be shorter.

In this particular example, a moderate level of compression is applied, if you had more time (computer power) to count occurrences of words, you could increase the compression of this statement by pulling out the word "is". But even large amounts of CPU time can only compress documents a fraction further, leaps from 110 MB to 22 MB aren't possible unless there are a lot of things to replace in the first compression pass..

Answer 6

Well, of course we can't compress an already compressed file. But still, believe me. A compressed file is way better and cheaper deal than being held up with no compression.

If it's just a matter of storage problem then I suppose you must buy a new sdcard/pen drive or must delete unwanted items and copies.

And if it's a matter of uploading then I prefer using a Wi-Fi and leaving your phone undisturbed if it will take half hour or more to upload.

Answer 7

First use the winrar to compress it with the best mode. Then archive it with 7zip. I tried it with gta sanandreas with a size 5.79 GB and after compression it got reduced to a memory of 12MB. Believe me, it's working.