Logging in an AVAssetWriter's finishWritingWithCompletionHandler block will cause a crash.

[stevemckenzie]

The crash occurs when using the deprecated function of getting the current queue.

A simple workaround is to do a dispatch_async on the main queue to execute the log there.

[kolyuchiy]

Something similar here. Logging from dispatch source queue will crash when compiled for iOS 6:

* thread #16: tid = 0x2327, 0x3c4e1162 libdispatch.dylib`_os_object_retain + 38, stop reason = EXC_BREAKPOINT (code=EXC_ARM_BREAKPOINT, subcode=0xdefe)
    frame #0: 0x3c4e1162 libdispatch.dylib`_os_object_retain + 38
    frame #1: 0x002251f4 XXX`-[DDLogMessage initWithLogMsg:level:flag:context:file:function:line:tag:options:](self=0x1e931010, _cmd=0x004ce66e, msg=0x1e930fb0, level=15, flag=8, context=0, aFile=0x004f00d5, aFunction=0x004c8f1b, line=162, aTag=0x00000000, optionsMask=0) + 644 at DDLog.m:873
    frame #2: 0x002230fc XXX`+[DDLog log:level:flag:context:file:function:line:tag:format:](self=0x005829d0, _cmd=0x004c18f5, asynchronous='\x01', level=15, flag=8, context=0, file=0x004f00d5, function=0x004c8f1b, line=162, tag=0x00000000, format=0x00588ad4) + 332 at DDLog.m:293
    frame #3: 0x001b5246 XXX`-[ZZZ](self=0x1e995560, _cmd=0x004c8f1b, error=0x0463aef4) + 302 at AAA.m:162
    frame #4: 0x001b4fe2 XXX`__61-[YYY]_block_invoke46(.block_descriptor=0x1e931d90) + 182 at BBB.m:146
    frame #5: 0x3c4e148e libdispatch.dylib`_dispatch_source_invoke + 258
    frame #6: 0x3c4e3afc libdispatch.dylib`_dispatch_queue_drain + 80
    frame #7: 0x3c4e167c libdispatch.dylib`_dispatch_queue_invoke + 44
    frame #8: 0x3c4e4612 libdispatch.dylib`_dispatch_root_queue_drain + 210
    frame #9: 0x3c4e47d8 libdispatch.dylib`_dispatch_worker_thread2 + 92
    frame #10: 0x3c5087f0 libsystem_c.dylib`_pthread_wqthread + 360

[bpoplauschi]

I think this is fixed in #121