Some links to read more about this,

ffmpeg (LGPL): https://ffmpeg.org/trac/ffmpeg/ticket/1229

vlc (LGPL): http://waffle.wootest.net/2011/01/08/vlc-gpl-tuaw-wtf/

This is a frequently repeated oversimplification. (L)GPL is not incompatible with iOS, it is incompatible with the Apple App Store.

It is fully, 100% GPL-compliant to release a (L)GPL'd iOS application linked to a (L)GPL'd library, as source code, with instructions on how to build and load on your iOS device.

It is /probably/ not compliant to distribute that through the App Store, though there is some disagreement, and it has never been taken to court.

It is /definitely/ not compliant to distribute a proprietary app that links to an (L)GPL'd library through the App Store, since Apple only permits static linking.