From some previous places in this thread:
QUOTE
For people who just want a no-nonsense movie player, I believe RealPlayer 10 will be better than QuickTime Player; you don't have to pay for full screen, and the full screen UI is pleasant and intuitive.
You don't have to pay for it using QuickTime either, it supports full-screen playback out of the box, it's just not implemented in the GUI. Everything is easily changed via osascript AppleScript.
Long before UNIX-based Mac OS, a Mac OS application's AppleScript dictionary was the equivalent of it's CLI, and is often the only way to use some features.
There are also free (donation-ware) QT front-ends like
Cellulo and a myriad of free and open-source players that wrap QT...
QUOTE
However, the one big plus about it that I am surprised nobody has mentioned: it plays HE-AAC, which no other player (that I'm aware of) can do on OS X.
FAAD works fine on OS X, and the latest versions support HE-AAC. FAAD can used by XMMS, as well as MPlayer, both of which also work on OS X. There is also a native Darwin CoreAudio XMMS output plug-in.
I also don't want to knock the Real guys, but until the OS X community is provided with either a native QTX QuickTime extension, or a native binary library as an OS X Framework that would allow dynamic linking with third-party applications, it won't gain the user-support and popularity of other codecs.
Right now on Mac OS X, the only common video-file problems I have are lacking support from Real codecs and Microsoft WMV9, which are not supported via QuickTime extensions and don't seem to have libraries or Frameworks usable by software like MPlayer.
I haven't yet tried RP10, but I assume I read it's "QuickTime" support as it operates as a wrapper for QT that also supports playback of Real files, rather than implementing the Real codecs as a native QuickTime component. I really hope someone will tell me I'm incorrect.
Edit 1: Modified formatting and spelling.
Edit 2: doh.