Keep reading for two tips on reducing the size of your iPhone apps.

1. Pack images together offline

By store related images on a single image “atlas” with an offline image packing tool, you can save precious disk space, as you get rid of the overhead of multiple image file headers. As a collateral benefit, you also get a loading time speed up (it’s faster to load a single big image than multiple small ones). Also, if you have many PNG32 images (as in a hidden-object game), consider packing them into two JPEG atlases. That’s what we did for Herod’s Lost Tomb:

By packing all hidden objects from each level into two color and an alpha JPEG images, the combined size of each level’s hidden objects on disk was reduced from ~800 KB to ~250-300 KB.

 
2. Use compressed audio wherever possible

Most developer default to AAC files for music and CAF files for sound effects. Although the playback of both formats are reportedly hardware accelerated on the iPhone, only the former is a compressed format. Why does that matter? Well, because you are probably more worried about disk size than ultra-low CPU usage, you might want to ditch CAF files in favor of OGG/Vorbis ones. It’s relatively easy to implement a sound engine around OpenAL and libogg. By converting a sound effect of, say, 4 seconds at 22Khz and 16 bit from CAF to OGG, you would be saving around 180 KB of space (200 KB – 20 KB). Multiply that by the number of sound effects used in your game and you will quickly realize you that converting all sfx to OGG would tranlate into savings of one to two megabytes.

If you know of other techniques to optimize app size, we’d love to hear them.

What can analytics/metrics software do for you? They track how your application is being used, and log things such as the number of unique users, how much time was spent on certain parts of the user interface, what features are they using the most, how many times the app crashed, etc. All these stats tell you which areas of your application you should improve.

Interestingly, most of the metrics tracking solutions out there do also offer ad placement services. This is an alternative business model to paid apps, although you will probably need tens of thousands of downloads to make some money out of it.

After a little research on each solution provider, I have put together the following matrix:

Unfortunately, I have not been able to test all solutions in depth. Therefore, I am not aware of which providers offers the best analytics module, or which SDK is more solid. Also lacking from the matrix are the minimum or average PPC or CPM revenue ratios.

If you find innaccurate or missing information, please leave a comment below and I will gladly update the matrix.

[Update 01/01/09] : Thanks to the commenters for pointing out Greystripe and Videoegg. I will update the matrix as soon as I can look into their iPhone services. Also according to people in the known, AppLoop has gone out of business, and their website is no longer accessible.

[Update 17/01/09] : Added Greystrip, Videoegg and Flurry to the matrix. Removed AppLoop (went out of business).