7zip compression parameters ?



  • Heya. I'm actually trying to save space on my HD by compressing the files I don't use, like video, .exe, .isos, etc.. But, sometimes, the compression didn't work well, and I just earn ~1-5% of the original size. Sometimes, the compressed file is heavier than the original. I'm using 7zip, and when I search, I learned that 7zip: - Save more place than the .zip with some ninja skills, and is more better in most plans (max. compressed size file, AES 256, multithreading, opensource...), but take much time to compress; - Save more place on "repetitive paterns", like if I have a 1Mo .txt file with just one word repeated again and again, I'll get a 1Ko .7zip file : 7zip detect the identical data segments; - Have some powerful compression algorithm for the .exe files (BCJ); - Often, the compression's effects change file from one file to another. I tried a bit of everything, but I don't really get great results. So, do you have "optimal parameters" for video, audio or anything compression ? I wonder if, for audio and video, it's really useful, because audio and video are already compressed. And I should also inform me about it, but I think I prefer to have a compressed file with HD video inside, rather than a LD video.



  • Sorry to say that, but there is hardly any chance to compress the already highly compressed video and audio files any further. The lossy compressors used to save them as mp3 or mp4, ogg, etc. are highly optimized for that purpose. Aditionally those work with prediction and block sizes to get even better results. 7zip is always lossless and can't get any better because of that.

    The only thing that could save some few MB is packing multiple files into one solid archive, which would reduce the overhead of not 100% filled sectors in the file system, but I don't think it is worth the effort.

    If you want to get smaller file sizes you should recompress the audio or video files to either/or
    [ul]

    • a different and better format like e.g. mp3 to mp4 with AAC & vbr,
    • xvid or normal low compressed AVI to mp4 h264 or WebM
    • to lower bitrates
    • bigger distances between the keyframes.
      [/ul]
      Each of these measures can reduce the file size.

    Keep in mind, that in all cases you will loose some quality because of requantization or lower bitrates or more lossyness.
    You'll have to do some experiments to find out, which losses you don't see or hear or to which level losses are acceptable for you.

    One last pitfall to avoid:
    There is no one method fits all material. For best results you will have to test it for every video or audio file again …



  • Yup, it's what i've read after posting. I had a little hope that I can, like I said, compress a video rather than get an low quality video, but finaly I'll just reduce the quality for the video, and pack the rest.

    Thanks you for responding anyway /o/


  • Vivaldi Translator

    QuHno, covered it very well, but I thought I would add some practical tips.
    First of all, anything is better than ZIP.

    Variable Bitrate (VBR) MP4 is your current best option to save space.
    It takes longer to encode, but the quality is higher at a smaller size.

    The best and easiest tool I have used for video/DVD encoding is Ahead "Nero Recode".
    There are many free tools that will do just as good, but Recode offers features they lack.
    Nero Recode will let you quickly see how big the file is if you want a certain quality, or if you want a certain size to see if the quality will be good enough.
    (other programs give you a calculator you type in).
    It lets you keep multiple audio-tracks and subtitles, and unlike the rest also includes the chapter marks for easy navigation.

    Music.
    Well if MP4/AAC is fine for you and you can do without MP3, think carefully about converting.
    MP3 also comes as VBR, so if you need to use MP3 this would be better.
    CD quality = about 170k if it were an MP3.
    MP3 does not have 170k as a step, so most people convert their CDs at 160 or 192k CBR (Constant Bitrate).
    If you have any music converted from CDs as 320k MP3, these will be the best to convert as they are taking more space than they need.

    VBR encoding, allows a minimum and maximum bitrate (audio and video).
    A quiet section or speech only requires a low bitrate. In video a still scene with minimal changes requires a low bitrate.
    Loud or complex sounds, fast motion or colour changes require higher bitrates.

    Nero MP4/AAC http://www.audiocoding.com/nero_aacenc.html
    What you need to know about MP3 https://vivaldi.net/blogs/entry/audio-encoding



  • try…...7zip command line

    William



  • @cyElAE:

    So, do you have "optimal parameters" for video, audio or anything compression ?

    If your problem is the space occupied on the data HDD or partition you should look at the deduplication, not compression.

    You can enable it on win8/win8.1/win10 and is pretty effective.

    I have freed over 600GB of spaceover 3.6GB of data (1/3 videos, 1/3 Iso, 1/3 generic documents)


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