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Compressing Beatmap Files

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↱ Fitting the Size-limit

How to make your map fit the size limitations: Compression by: ziin

Osu! maps, according to the current ranking guidelines, must be under 10 MB, or 24 MB if the song has a video. In this tutorial I will tell you smart ways to get your map under that limit.

There are 2 types of compression. Lossy and Lossless compression.

  • Lossless implies that the quality never degrades and can be repeatedly compressed or decompressed.
  • Lossy is a much more powerful form of compression which sacrifices quality for space/processor demand.



The *.osz package is actually a *.zip file, and will compress your beatmap, although not very much, since audio, video, and images are usually compressed very well. Zip and other archives are all lossless compression, otherwise you wouldn't be able to get your data back.


Recommended reading: Encoding Video.

Videos are usually where people go wrong. There are thousands of video codecs out there, and believe it or not, YouTube is usually a terrible place to get videos. For the best quality, you should always downsize from a high resolution source (720p YouTube videos are fine for this).

h.264 and XviD are very good codecs to use but like most video codecs, they are lossy. So do not re-encode multiple times, but encode from the high resolution source.


Now that there is a limit on audio bitrate, it's not as much of a problem anymore. However long songs at 192 kbps will undoubtedly take up most of your space. I recommend using a variable bitrate between rate factor 2 and 5 (I try to stick around 4). With a variable bitrate, you get more compression in low activity areas, and more quality in higher areas.

CBF 01.png

Programs such as Audacity 1.3.13 does an excellent job of saving variable bitrate audio with the correct plugins.

Osu accepts 2 major file formats: mp3 and ogg vorbis. Vorbis has a clear advantage over mp3 at low bitrates (under 128 kbps), but suffers from lack of support by proprietary software like apple, since mp3 is the standard for audio. However, there are severely limiting returns on using anything higher than 128 kbps. For osu! it doesn't really matter which one you use.


There are 2 major image formats which make up most of the images you find online: jpg and png. Png uses lossless compression which makes it ideal for small and or simple images. Complex images are better suited for jpg. The majority of image editing programs however do not naturally use *.png and *.jpg compression to the most of their ability however, leaving you with 4 KB pngs of 1 color, which could be compressed up to 400 times smaller.

Gimp actually does a good job with *.jpg files.

CBF 02.png

There are four important things to check: Optimize, Progressive, subsampling, and quality. Optimize is just a way to compress the *.jpg without losing quality and should always be checked. Progressive is a method to make jpgs "fade in" when downloaded from the internet. It has a side effect of making the image smaller so long as the image is over 20 KB. Subsampling is a way to improve quality or compression. No subsampling (1x1) will make text and lines much clearer at the cost of space. 2x2 subsampling does very well for photographs which do not have distinct lines (like text). Quality is the easiest way to keep the image looking good. I use 95, since the gains after 95 aren't really worthwhile.

Pngs are actually much simpler to compress, but GIMP does not do it very well. Optipng and Pngout are two of the best tools to compress *.png files. Optipng can find the optimum settings for the *.png, and pngout re-compresses the image using *.kzip. Often times just using pngout will reduce the image size by 20%.

CBF 03.png

For even better compression, you can use a script which combines multiple compressors and brute forces close to the smallest file possible. The script's name is pngslim.

CBF 04.png


So there you have it.

CBF 05.png

List of Guides in osu!
FAQ/Ranking Guidelines
General Mapping Guides What is a beatmap? How do I beatmap? How do beatmaps get ranked? Difficulty appropriate gameplay elements How to time songs Song Setup Mapping Taiko Difficulties Fitting the Size-limit
Modding Aides AIBat
Mapping Techniques Mapping Techniques Making Good Sliders How to do 15° Patterns
Modding Info How do I mod?
Skinning/Hitsound Guides

Cropping with Complex Backgrounds Cropping with Simple Backgrounds Making Properly Centered Spinners What are Custom Sample Overrides? Custom Hitsound Library Adding custom hitsounds

Storyboarding Guides Storyboard Scripting Storyboard Scripting (Cheat Sheet) SGL Tool Reducing SB Load
Audio Editing Guides Audio editing Basic MP3 modifications Getting songs from Video Games
Video Editing Guides Compressing Videos Videos from YouTube
Gameplay Guides Play Styles How to increase your rank Making nice recording for Youtube Live streaming osu! How do I use the Chat Console?
Common Mistakes Changing the Map's Artist or Title
osu!forums Guides BBCode Starting a Beatmap Project How to not Embarrass Yourself in the Projects Subforum How to not Embarrass Yourself in the Modding Queues Subforum
Miscellaneous BanchoBot Changing Title Text Music Theory Setting the Offset on the Correct Beat Collab Information Shortcut Key Reference GL Support Issues What is Internet Relay Chat? How to Run osu! on Your Mac without using Boot Camp

Contents of
Getting Started Registration Installation Newbie's guide Game Interface Options Hit Objects
osu! Game Styles Basic explanation Multi-play
External ports » osu!stream osu!droid opsu! osu!wp T-Aiko Beats
External clients » osu!tourney osu!MapDownloader
World of osu!
Miscellaneous » Mascots osu!academy osu!talk
Beatmap Editor Compose / Design (Scripting) / Timing / Song Setup

Beatmapping Beat Snap Divisor / Distance Snap Custom Sample Overrides Kiai Time Mapping Techniques Skinning Skin.ini Storyboarding

Online Editing
and Ranking
Beatmap forum Submission Beatmap Approval (How to Get Your Map Ranked) Modding (Getting Your Map Modded) Music Theory Audio Editing Kudosu / Star Priority
People The Team Administrators/Global Moderation Team Quality Assurance Team Beatmap Nomination Group Language Moderators osu! Alumni Support Team Community Contributors List of notable people