I got build failure reports from various people for SDL-mixer on OS X when compiling in 64bit mode, both in 10.5 and 10.6. The reason: Deprecated QuickTime APIs that have been removed for 64bit binaries, see below.

Proposed short-term workaround: Disable or just remove the crappy "native" MIDI code. It's rather bad anyway (I should know, i wrote it ;).

Mid/long-term solution: Write new CoreAudio based code to replace it. That code then would work on all OS X versions (well, at least on 10.4 upwards for sure), be more accurate, sound better and take up less system resources. And be simpler, did I mention that? Generating MIDI output with CoreAudio is pretty easy, we do it in ScummVM, Exult, Pentagram, DOSBox, ... 

Here are the build errors:

gcc -I/sw64/include -D_GNU_SOURCE=1 -I/sw64/include/SDL -D_GNU_SOURCE=1 -D_THREAD_SAFE -DCMD_MUSIC -DWAV_MUSIC -DMOD_MUSIC -I./mikmod -DMID_MUSIC -DUSE_TIMIDITY_MIDI -I./timidity -DUSE_NATIVE_MIDI -I./native_midi -DOGG_MUSIC -DMP3_MUSIC -I/sw64/include -I/sw64/include/smpeg -I/sw64/include/SDL -D_GNU_SOURCE=1 -D_THREAD_SAFE -c ./native_midi/native_midi_mac.c  -fno-common -DPIC -o build/.libs/native_midi_mac.o
./native_midi/native_midi_mac.c:51: error: 'NoteRequest' undeclared here (not in a function)
./native_midi/native_midi_mac.c:79: error: syntax error before 'gTunePlayer'
./native_midi/native_midi_mac.c:79: warning: initialization makes integer from pointer without a cast
./native_midi/native_midi_mac.c:79: warning: data definition has no type or storage class
./native_midi/native_midi_mac.c: In function 'native_midi_loadsong':
./native_midi/native_midi_mac.c:134: warning: comparison between pointer and integer
./native_midi/native_midi_mac.c:135: error: 'kTunePlayerComponentType' undeclared (first use in this function)
./native_midi/native_midi_mac.c:135: error: (Each undeclared identifier is reported only once
./native_midi/native_midi_mac.c:135: error: for each function it appears in.)
./native_midi/native_midi_mac.c:135: warning: assignment makes integer from pointer without a cast
./native_midi/native_midi_mac.c: In function 'native_midi_loadsong_RW':
./native_midi/native_midi_mac.c:197: warning: comparison between pointer and integer
./native_midi/native_midi_mac.c:198: error: 'kTunePlayerComponentType' undeclared (first use in this function)
./native_midi/native_midi_mac.c:198: warning: assignment makes integer from pointer without a cast
./native_midi/native_midi_mac.c: In function 'native_midi_freesong':
./native_midi/native_midi_mac.c:239: warning: comparison between pointer and integer
./native_midi/native_midi_mac.c:241: warning: passing argument 1 of 'CloseComponent' makes pointer from integer without a cast
./native_midi/native_midi_mac.c:242: warning: assignment makes integer from pointer without a cast
./native_midi/native_midi_mac.c: In function 'native_midi_start':
./native_midi/native_midi_mac.c:251: warning: comparison between pointer and integer
./native_midi/native_midi_mac.c:260: error: 'kTuneStartNow' undeclared (first use in this function)
./native_midi/native_midi_mac.c: In function 'native_midi_stop':
./native_midi/native_midi_mac.c:310: warning: comparison between pointer and integer
./native_midi/native_midi_mac.c: In function 'native_midi_active':
./native_midi/native_midi_mac.c:322: warning: comparison between pointer and integer
./native_midi/native_midi_mac.c:324: error: 'TuneStatus' undeclared (first use in this function)
./native_midi/native_midi_mac.c:324: error: syntax error before 'ts'
./native_midi/native_midi_mac.c:326: error: 'ts' undeclared (first use in this function)
./native_midi/native_midi_mac.c: In function 'native_midi_setvolume':
./native_midi/native_midi_mac.c:335: warning: comparison between pointer and integer
./native_midi/native_midi_mac.c: In function 'BuildTuneSequence':
./native_midi/native_midi_mac.c:432: error: 'kFirstDrumkit' undeclared (first use in this function)
./native_midi/native_midi_mac.c:434: error: 'kFirstGMInstrument' undeclared (first use in this function)
./native_midi/native_midi_mac.c:504: error: 'kControllerVolume' undeclared (first use in this function)
./native_midi/native_midi_mac.c:516: error: 'kControllerPan' undeclared (first use in this function)
./native_midi/native_midi_mac.c:567: error: 'kControllerPitchBend' undeclared (first use in this function)
./native_midi/native_midi_mac.c:618: error: 'kEndMarkerValue' undeclared (first use in this function)
./native_midi/native_midi_mac.c: In function 'BuildTuneHeader':
./native_midi/native_midi_mac.c:627: error: 'myNoteRequest' undeclared (first use in this function)
./native_midi/native_midi_mac.c:628: error: 'NoteAllocator' undeclared (first use in this function)
./native_midi/native_midi_mac.c:628: error: syntax error before 'myNoteAllocator'
./native_midi/native_midi_mac.c:633: error: 'myNoteAllocator' undeclared (first use in this function)
./native_midi/native_midi_mac.c:638: error: 'kNoteAllocatorComponentType' undeclared (first use in this function)
./native_midi/native_midi_mac.c:661: error: 'kGeneralEventNoteRequest' undeclared (first use in this function)
./native_midi/native_midi_mac.c:662: error: syntax error before ')' token
./native_midi/native_midi_mac.c:688: error: 'kEndMarkerValue' undeclared (first use in this function)
make: *** [build/native_midi_mac.lo] Error 1
### execution of make failed, exit code 2
"