I'm doing most of my VLC development with Ubuntu Linux. Unfortunately, the latest Ubuntu version (9.04, aka Jaunty Jackalope) comes with Qt version 4.5.0. This version contains some bugs which make it undesirable for use with VLC. Many bugs have been subsequently fixed in 4.5.1, so I decided to use that instead.
I downloaded and installed the latest Qt SDK, a fairly straightforward process. It defaults to installing in /opt/qtsdk-2009.02 which was fine with me. Next, I had to try to get VLC to use this version of Qt instead of the standard Ubuntu version. This took a bit of figuring out, but eventually I found the QT4_CFLAGS and QT4_LIBS environment variables. After some trial and error, I found that the following commands did what I wanted:
export QT4_CFLAGS="-I/opt/qtsdk-2009.02/qt/include/ -I/opt/qtsdk-2009.02/qt/include/QtCore/ -I/opt/qtsdk-2009.02/qt/include/QtGui/"
export QT4_LIBS="-L/opt/qtsdk-2009.02/qt/lib/ -lQtCore -lQtGui"
I was then able to use ./configure && ./compile as normal to get VLC built against the newly installed Qt 4.5.1.
Update: xtophe pointed out in IRC that pkg-config files are distributed Qt. So a better solution is just to make sure pkg-config is able to find Qt's .pc files. I did this by setting the PKG_CONFIG_PATH environment variable:
export PKG_CONFIG_PATH=/opt/qtsdk-2009.02/qt/lib/pkgconfig/
