How do I solve unclear iOS crashes in crashlytics?

Question

This is an error I get in crashlytics:

Thread : Crashed: WebThread
0  libobjc.A.dylib                0x344e4f46 objc_msgSend + 5
1  UIKit                          0x295ebe51 +[UIViewAnimationState popAnimationState] + 320
2  MediaPlayer                    0x278278bb -[MPVolumeSlider _layoutForAvailableRoutes] + 1410
3  MediaPlayer                    0x27826505 -[MPVolumeSlider layoutSubviews] + 60
4  UIKit                          0x295b7023 -[UIView(CALayerDelegate) layoutSublayersOfLayer:] + 546
5  QuartzCore                     0x28fd7d99 -[CALayer layoutSublayers] + 128
6  QuartzCore                     0x28fd35cd CA::Layer::layout_if_needed(CA::Transaction*) + 360
7  UIKit                          0x295c9c03 -[UIView(Hierarchy) layoutBelowIfNeeded] + 138
8  UIKit                          0x295cf0a3 -[UISlider setValue:animated:] + 178
9  MediaPlayer                    0x27826bfb -[MPVolumeSlider volumeController:volumeValueDidChange:] + 78
10 MediaPlayer                    0x2788a995 -[MPVolumeController updateVolumeValue] + 252
11 MediaPlayer                    0x27826613 -[MPVolumeSlider didMoveToSuperview] + 126
12 UIKit                          0x295b5ec1 -[UIView(Hierarchy) _postMovedFromSuperview:] + 428
13 UIKit                          0x295c072b -[UIView(Internal) _addSubview:positioned:relativeTo:] + 1498
14 UIKit                          0x295c014b -[UIView(Hierarchy) addSubview:] + 30
15 MediaPlayer                    0x278293e9 -[MPVolumeView _createSubviews] + 236
16 MediaPlayer                    0x27828035 -[MPVolumeView _initWithStyle:] + 212
17 MediaPlayer                    0x278280c9 -[MPVolumeView initWithFrame:style:] + 80
18 MediaPlayer                    0x27828073 -[MPVolumeView initWithFrame:] + 38
19 UIKit                          0x295d7119 -[UIView init] + 44
20 WebCore                        0x32568435 -[WebMediaSessionHelper allocateVolumeView] + 264
21 WebCore                        0x325686e7 -[WebMediaSessionHelper initWithCallback:] + 394
22 WebCore                        0x32567811 WebCore::MediaSessionManageriOS::MediaSessionManageriOS() + 172
23 WebCore                        0x325676fd WebCore::MediaSessionManager::sharedManager() + 124
24 WebCore                        0x3256694d WebCore::MediaSession::MediaSession(WebCore::MediaSessionClient&) + 32
25 WebCore                        0x321f6935 WebCore::HTMLMediaSession::create(WebCore::MediaSessionClient&) + 20
26 WebCore                        0x321e5257 WebCore::HTMLMediaElement::HTMLMediaElement(WebCore::QualifiedName const&, WebCore::Document&, bool) + 1046
27 WebCore                        0x3220e3db WebCore::HTMLVideoElement::create(WebCore::QualifiedName const&, WebCore::Document&, bool) + 38
28 WebCore                        0x321d83a5 WebCore::videoConstructor(WebCore::QualifiedName const&, WebCore::Document&, WebCore::HTMLFormElement*, bool) + 56
29 WebCore                        0x321d7af9 WebCore::HTMLElementFactory::createElement(WebCore::QualifiedName const&, WebCore::Document&, WebCore::HTMLFormElement*, bool) + 232
30 WebCore                        0x31de00bd WebCore::HTMLDocument::createElement(WTF::AtomicString const&, int&) + 88
31 WebCore                        0x31ddffff WebCore::jsDocumentPrototypeFunctionCreateElement(JSC::ExecState*) + 242
32 JavaScriptCore                 0x273f6133 llint_entry + 21314
33 JavaScriptCore                 0x273f5d27 llint_entry + 20278
34 JavaScriptCore                 0x273f5d27 llint_entry + 20278
35 JavaScriptCore                 0x273f5d27 llint_entry + 20278
36 JavaScriptCore                 0x273f5d27 llint_entry + 20278
37 JavaScriptCore                 0x273f0bdf callToJavaScript + 334
38 JavaScriptCore                 0x273803b5 JSC::JITCode::execute(JSC::VM*, JSC::ProtoCallFrame*) + 36
39 JavaScriptCore                 0x271ccda7 JSC::Interpreter::executeCall(JSC::ExecState*, JSC::JSObject*, JSC::CallType, JSC::CallData const&, JSC::JSValue, JSC::ArgList const&) + 350
40 JavaScriptCore                 0x272c20dd JSC::call(JSC::ExecState*, JSC::JSValue, JSC::CallType, JSC::CallData const&, JSC::JSValue, JSC::ArgList const&, JSC::JSValue*) + 64
41 WebCore                        0x31dd9d6d WebCore::ScheduledAction::executeFunctionInContext(JSC::JSGlobalObject*, JSC::JSValue, WebCore::ScriptExecutionContext*) + 368
42 WebCore                        0x31dd9a53 WebCore::ScheduledAction::execute(WebCore::Document*) + 114
43 WebCore                        0x31dd9475 WebCore::DOMTimer::fired() + 460
44 WebCore                        0x31dd8f4d WebCore::ThreadTimers::sharedTimerFiredInternal() + 132
45 WebCore                        0x31dd8ea9 WebCore::timerFired(__CFRunLoopTimer*, void*) + 24
46 CoreFoundation                 0x25f2aedf __CFRUNLOOP_IS_CALLING_OUT_TO_A_TIMER_CALLBACK_FUNCTION__ + 14
47 CoreFoundation                 0x25f2aa5b __CFRunLoopDoTimer + 650
48 CoreFoundation                 0x25f28cab __CFRunLoopRun + 1418
49 CoreFoundation                 0x25e75201 CFRunLoopRunSpecific + 476
50 CoreFoundation                 0x25e75013 CFRunLoopRunInMode + 106
51 WebCore                        0x31e3e183 RunWebThread(void*) + 418
52 libsystem_pthread.dylib        0x34bace23 _pthread_body + 138
53 libsystem_pthread.dylib        0x34bacd97 _pthread_start + 118

Can anyone explain how do I start working on that crash?

I can't even see on what page it happened or what was the last action the user took...

I'm pretty sure it has to do something with a video i'm playing at the beginning of the app but I have no idea what's the issue that causes the crash...

Answer 1

It's a bug introduced in iOS 8 and fixed in iOS 9. Here's some more info: https://bugs.webkit.org/show_bug.cgi?id=138971