This only happens with http sources, file and rtsp both threw media unavailable exceptions as expected.

The On2 QuickTime importer crashes thusly (inside FXM_MovieImportValidateDataRef, which is in a QuickTime component supplied by On2):

Exception Type: EXC_BAD_ACCESS (SIGBUS)
Exception Codes: KERN_PROTECTION_FAILURE at 0x000000000000002c
Crashed Thread: 0 Dispatch queue: com.apple.main-thread

Thread 0 Crashed: Dispatch queue: com.apple.main-thread
0 com.apple.QuickTime 0x94cb4912 QTMLGrabMutex + 18
1 com.apple.QuickTime 0x94e41655 QTWorkContextCopyForMediaContextID + 28
2 ...uickTimeStreaming.component 0x12adc261 HTTPDhlr_CheckForFatalError + 254
3 ...uickTimeStreaming.component 0x12adc312 HTTPDhlr_ReadSYNC + 165
4 ...uickTimeStreaming.component 0x12adf146 HTTPDataHandler_ScheduleData64 + 449
5 ...uickTimeStreaming.component 0x12adf52b HTTPDataHandler_ScheduleData + 72
6 ...ple.CoreServices.CarbonCore 0x937bda81 callComponentStorage_4444444 + 63
7 ...ple.CoreServices.CarbonCore 0x937b2474 CallComponentFunctionCommonWithStorage(char**, ComponentParameters*, long (*)(), unsigned long) + 54
8 ...uickTimeStreaming.component 0x12adcd09 HTTPDataHandler_ComponentDispatch + 110
9 ...ple.CoreServices.CarbonCore 0x937aab06 CallComponentDispatch + 29
10 com.apple.QuickTime 0x94f31390 DataHScheduleData + 73
11 JMCServer 0x00005163 FXM_MovieImportValidateDataRef + 147
12 ...ple.CoreServices.CarbonCore 0x937bd58f callComponentStorage_4444 + 42
13 ...ple.CoreServices.CarbonCore 0x937b2474 CallComponentFunctionCommonWithStorage(char**, ComponentParameters*, long (*)(), unsigned long) + 54
14 JMCServer 0x0000533a FXM_MovieImportComponentDispatch + 138
15 ...ple.CoreServices.CarbonCore 0x937aabc8 CallComponent + 192
16 ...ple.CoreServices.CarbonCore 0x937aab06 CallComponentDispatch + 29
17 com.apple.QuickTime 0x94f31fa1 MovieImportValidateDataRef + 55
18 com.apple.QuickTime 0x94cddaba GetMovieImporterForDataRef_priv + 2282
19 com.apple.QuickTime 0x94d37c81 CanQuickTimeOpenEverything + 1983
20 com.apple.QuickTime 0x94d374b7 CanQuickTimeOpenDataRef_priv + 58
21 com.apple.QuickTime 0x94d3746e CanQuickTimeOpenDataRef + 57
22 com.apple.QTKit 0x91c24df1 +[QTMovie_QuickTime canInitWithDataReference:fileTypes:error:] + 206
23 com.apple.QTKit 0x91bfef2b +[QTMovie canInitWithURL:fileTypes:] + 56
24 com.apple.QTKit 0x91bfefd7 +[QTMovie canInitWithURL:] + 49
25 com.apple.CoreFoundation 0x9337405d __invoking___ + 29
26 com.apple.CoreFoundation 0x93373fc8 -[NSInvocation invoke] + 136
27 com.apple.CoreFoundation 0x933aff28 -[NSInvocation invokeWithTarget:] + 72
28 com.apple.CoreFoundation 0x93374e54 ___forwarding___ + 1108
29 com.apple.CoreFoundation 0x93374982 _CF_forwarding_prep_0 + 50
30 com.apple.CoreFoundation 0x9337405d __invoking___ + 29
31 com.apple.CoreFoundation 0x93373fc8 -[NSInvocation invoke] + 136
32 com.apple.Foundation 0x96f8982a -[NSConnection dispatchInvocation:] + 476
33 com.apple.Foundation 0x96f87fad -[NSConnection handleRequest:sequence:] + 1432
34 com.apple.Foundation 0x96f81db6 -[NSConnection handlePortCoder:] + 951
35 com.apple.Foundation 0x96f819e5 -[NSConcretePortCoder dispatch] + 160
36 com.apple.Foundation 0x96f68ff1 __NSFireMachPort + 325
37 com.apple.CoreFoundation 0x9333cb72 __CFMachPortPerform + 338
38 com.apple.CoreFoundation 0x933388db __CFRunLoopRun + 6523
39 com.apple.CoreFoundation 0x93336864 CFRunLoopRunSpecific + 452
40 com.apple.CoreFoundation 0x93336691 CFRunLoopRunInMode + 97
41 com.apple.Foundation 0x96f4137c -[NSRunLoop(NSRunLoop) runMode:beforeDate:] + 279
42 com.apple.Foundation 0x96f96380 -[NSRunLoop(NSRunLoop) runUntilDate:] + 79
43 JMCServer 0x00001f3a main + 420 (JMCServerMain.m:66)
44 JMCServer 0x00001d7b _start + 209
45 JMCServer 0x00001ca9 start + 41