Works here. I'm using the mplayer backend.
Do you use kdemultimedia-mplayerthumbs or ffmpegthumbs? Try installing the first (and removing the second)

Also, run mplayerthumbsconfig and set the backend to MPlayer. (that works with mplayer2 too)

That works beautifully. It made using dolphin as a file manager impossible when I couldn't even try to open the .avi file. It also seems to happen *only* with .avi files. I tried other formats like .mpeg, .flv, and so on. It *only* happened with .avi. Strangely if I ran dolphin from a console it worked fine, and it seemed to only crash when launched from the KDE Menu. I googled for similar problems as this, and they date back to before 2010 and seemed to have been linked to dbus issues, which wasn't what I was experiencing. I did as you instructed and it seems to have fixed the issue. If it does crash again, I'll be sure to grab another backtrace. So far so good.

Nix that, I spoke too soon. It's doing it *again*. Same issue now. I start dolphin from the menu, it loads, I hover my mouse over the .avi file and it crashes it. Now, I've tried renaming the .avi file just in case that may have some effect, and it doesn't. Except this time if I enable Preview, close dolphin, reopen it, it will crash. If I disable Preview, close dolphin and reopen it, it will still crash. And it crashes every time, same as before. Except it *seems* to alternate between the conditions; eg. Preview enabled, closed, and reopened Dolphin - it will crash the first time, but then reopen dolphin again and it works fine. Repeat the process but this time disabling preview, close dolphin and reopen, it will crash. But then open Dolphin again, enable preview (when preview was previously disabled and caused the crash), it will crash. So this seems to work but only if preview is *already* enabled, having already crashed once, and reopen dolphin with Preview already on and it will work.

-----Backtrace with Preview enabled, dolphin closed and reopened with Preview already enabled-------
Application: Dolphin (kdeinit4), signal: Aborted
[Current thread is 1 (Thread 0x7f6644259760 (LWP 3377))]

Thread 3 (Thread 0x7f662a986700 (LWP 3379)):
#0 0x00007f664195b4fb in ?? () from /lib/libc.so.6
#1 0x00007f66418f5eef in ?? () from /lib/libc.so.6
#2 0x00007f66418f4301 in free () from /lib/libc.so.6
#3 0x00007f663571211c in ?? () from /usr/lib/libnvidia-tls.so.275.09.07
#4 0x00007f6642f06005 in ?? () from /usr/lib/libQtCore.so.4
#5 0x00007f663e995f24 in g_main_context_check () from /usr/lib/libglib-2.0.so.0
#6 0x00007f663e9967f2 in ?? () from /usr/lib/libglib-2.0.so.0
#7 0x00007f663e996d09 in g_main_context_iteration () from /usr/lib/libglib-2.0.so.0
#8 0x00007f6642f06876 in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQtCore.so.4
#9 0x00007f6642edadb2 in QEventLoop::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQtCore.so.4
#10 0x00007f6642edafb7 in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQtCore.so.4
#11 0x00007f6642df269f in QThread::exec() () from /usr/lib/libQtCore.so.4
#12 0x00007f6642ebdd8f in ?? () from /usr/lib/libQtCore.so.4
#13 0x00007f6642df50f5 in ?? () from /usr/lib/libQtCore.so.4
#14 0x00007f66366dfbc3 in ?? () from /usr/lib/libGL.so.1
#15 0x00007f6642b6bd40 in start_thread () from /lib/libpthread.so.0
#16 0x00007f664194eaed in clone () from /lib/libc.so.6
#17 0x0000000000000000 in ?? ()

Thread 2 (Thread 0x7f6629d96700 (LWP 3392)):
[KCrash Handler]
#6 0x00007f66418b1705 in raise () from /lib/libc.so.6
#7 0x00007f66418b2b7b in abort () from /lib/libc.so.6
#8 0x00007f66418ea5a3 in ?? () from /lib/libc.so.6
#9 0x00007f66418f042a in ?? () from /lib/libc.so.6
#10 0x00007f66418f2ee7 in ?? () from /lib/libc.so.6
#11 0x00007f66418f4479 in realloc () from /lib/libc.so.6
#12 0x00007f66366db470 in ?? () from /usr/lib/libGL.so.1
#13 0x00007f66366df93d in ?? () from /usr/lib/libGL.so.1
#14 0x00007f66366d9d95 in ?? () from /usr/lib/libGL.so.1
#15 0x00007f66440968fe in dl_open_worker () from /lib/ld-linux-x86-64.so.2
#16 0x00007f66440926d6 in _dl_catch_error () from /lib/ld-linux-x86-64.so.2
#17 0x00007f66440963da in _dl_open () from /lib/ld-linux-x86-64.so.2
#18 0x00007f663f695f26 in ?? () from /lib/libdl.so.2
#19 0x00007f66440926d6 in _dl_catch_error () from /lib/ld-linux-x86-64.so.2
#20 0x00007f663f6964cf in ?? () from /lib/libdl.so.2
#21 0x00007f663f695fc1 in dlopen () from /lib/libdl.so.2
#22 0x00007f663bb17b27 in ?? () from /usr/lib/libstreamanalyzer.so.0
#23 0x00007f663bb18336 in ?? () from /usr/lib/libstreamanalyzer.so.0
#24 0x00007f663bb400df in ?? () from /usr/lib/libstreamanalyzer.so.0
#25 0x00007f663bb402c1 in Strigi::StreamAnalyzer::StreamAnalyzer(Strigi::AnalyzerConfiguration&) () from /usr/lib/libstreamanalyzer.so.0
#26 0x00007f663c3dfb5d in ?? () from /usr/lib/libkio.so.5
#27 0x00007f663c3e0a47 in KFileMetaInfo::KFileMetaInfo(QString const&, QString const&, QFlags<KFileMetaInfo::What>) () from /usr/lib/libkio.so.5
#28 0x00007f663c4ae73c in ?? () from /usr/lib/libkio.so.5
#29 0x00007f6642df50f5 in ?? () from /usr/lib/libQtCore.so.4
#30 0x00007f66366dfbc3 in ?? () from /usr/lib/libGL.so.1
#31 0x00007f6642b6bd40 in start_thread () from /lib/libpthread.so.0
#32 0x00007f664194eaed in clone () from /lib/libc.so.6
#33 0x0000000000000000 in ?? ()

Thread 1 (Thread 0x7f6644259760 (LWP 3377)):
#0 0x00007f664195b4fb in ?? () from /lib/libc.so.6
#1 0x00007f66418f5eef in ?? () from /lib/libc.so.6
#2 0x00007f66418f4301 in free () from /lib/libc.so.6
#3 0x00007f663571211c in ?? () from /usr/lib/libnvidia-tls.so.275.09.07
#4 0x00007f6643706045 in XFreeGC () from /usr/lib/libX11.so.6
#5 0x00007f66421833f4 in QX11PixmapData::fromImage(QImage const&, QFlags<Qt::ImageConversionFlag>) () from /usr/lib/libQtGui.so.4
#6 0x00007f664216ed7f in QPixmap::fromImage(QImage const&, QFlags<Qt::ImageConversionFlag>) () from /usr/lib/libQtGui.so.4
#7 0x00007f6643c09605 in KIconEffect::apply(QPixmap const&, int, float, QColor const&, QColor const&, bool) const () from /usr/lib/libkdeui.so.5
#8 0x00007f6643c0989e in KIconEffect::apply(QPixmap const&, int, int) const () from /usr/lib/libkdeui.so.5
#9 0x00007f663c3d9146 in KFileItemDelegate::Private::applyHoverEffect(QPixmap const&) const () from /usr/lib/libkio.so.5
#10 0x00007f663c3ddf8d in ?? () from /usr/lib/libkio.so.5
#11 0x00007f6630c46e8b in ?? () from /usr/lib/libdolphinprivate.so.4
#12 0x00007f66425bf893 in QListView::paintEvent(QPaintEvent*) () from /usr/lib/libQtGui.so.4
#13 0x00007f66420ec652 in QWidget::event(QEvent*) () from /usr/lib/libQtGui.so.4
#14 0x00007f664248cba6 in QFrame::event(QEvent*) () from /usr/lib/libQtGui.so.4
#15 0x00007f664259c95b in QAbstractItemView::viewportEvent(QEvent*) () from /usr/lib/libQtGui.so.4
#16 0x00007f6642edbd48 in QCoreApplicationPrivate::sendThroughObjectEventFilters(QObject*, QEvent*) () from /usr/lib/libQtCore.so.4
#17 0x00007f664209c13f in QApplicationPrivate::notify_helper(QObject*, QEvent*) () from /usr/lib/libQtGui.so.4
#18 0x00007f66420a0fe1 in QApplication::notify(QObject*, QEvent*) () from /usr/lib/libQtGui.so.4
#19 0x00007f6643c629c6 in KApplication::notify(QObject*, QEvent*) () from /usr/lib/libkdeui.so.5
#20 0x00007f6642edbbbc in QCoreApplication::notifyInternal(QObject*, QEvent*) () from /usr/lib/libQtCore.so.4
#21 0x00007f66420e9584 in QWidgetPrivate::drawWidget(QPaintDevice*, QRegion const&, QPoint const&, int, QPainter*, QWidgetBackingStore*) () from /usr/lib/libQtGui.so.4
#22 0x00007f66420ea160 in QWidgetPrivate::paintSiblingsRecursive(QPaintDevice*, QList<QObject*> const&, int, QRegion const&, QPoint const&, int, QPainter*, QWidgetBackingStore*) () from /usr/lib/libQtGui.so.4
#23 0x00007f66420e92dc in QWidgetPrivate::drawWidget(QPaintDevice*, QRegion const&, QPoint const&, int, QPainter*, QWidgetBackingStore*) () from /usr/lib/libQtGui.so.4
#24 0x00007f66420ea160 in QWidgetPrivate::paintSiblingsRecursive(QPaintDevice*, QList<QObject*> const&, int, QRegion const&, QPoint const&, int, QPainter*, QWidgetBackingStore*) () from /usr/lib/libQtGui.so.4
#25 0x00007f66420e92dc in QWidgetPrivate::drawWidget(QPaintDevice*, QRegion const&, QPoint const&, int, QPainter*, QWidgetBackingStore*) () from /usr/lib/libQtGui.so.4
#26 0x00007f66420ea160 in QWidgetPrivate::paintSiblingsRecursive(QPaintDevice*, QList<QObject*> const&, int, QRegion const&, QPoint const&, int, QPainter*, QWidgetBackingStore*) () from /usr/lib/libQtGui.so.4
#27 0x00007f66420e92dc in QWidgetPrivate::drawWidget(QPaintDevice*, QRegion const&, QPoint const&, int, QPainter*, QWidgetBackingStore*) () from /usr/lib/libQtGui.so.4
#28 0x00007f66420ea160 in QWidgetPrivate::paintSiblingsRecursive(QPaintDevice*, QList<QObject*> const&, int, QRegion const&, QPoint const&, int, QPainter*, QWidgetBackingStore*) () from /usr/lib/libQtGui.so.4
#29 0x00007f66420e92dc in QWidgetPrivate::drawWidget(QPaintDevice*, QRegion const&, QPoint const&, int, QPainter*, QWidgetBackingStore*) () from /usr/lib/libQtGui.so.4
#30 0x00007f66420ea160 in QWidgetPrivate::paintSiblingsRecursive(QPaintDevice*, QList<QObject*> const&, int, QRegion const&, QPoint const&, int, QPainter*, QWidgetBackingStore*) () from /usr/lib/libQtGui.so.4
#31 0x00007f66420e92dc in QWidgetPrivate::drawWidget(QPaintDevice*, QRegion const&, QPoint const&, int, QPainter*, QWidgetBackingStore*) () from /usr/lib/libQtGui.so.4
#32 0x00007f66420ea160 in QWidgetPrivate::paintSiblingsRecursive(QPaintDevice*, QList<QObject*> const&, int, QRegion const&, QPoint const&, int, QPainter*, QWidgetBackingStore*) () from /usr/lib/libQtGui.so.4
#33 0x00007f66420e92dc in QWidgetPrivate::drawWidget(QPaintDevice*, QRegion const&, QPoint const&, int, QPainter*, QWidgetBackingStore*) () from /usr/lib/libQtGui.so.4
#34 0x00007f66422a5acd in ?? () from /usr/lib/libQtGui.so.4
#35 0x00007f66420dfde0 in QWidgetPrivate::syncBackingStore() () from /usr/lib/libQtGui.so.4
#36 0x00007f66420ecb6c in QWidget::event(QEvent*) () from /usr/lib/libQtGui.so.4
#37 0x00007f66424a62db in QMainWindow::event(QEvent*) () from /usr/lib/libQtGui.so.4
#38 0x00007f6643d5f49e in KXmlGuiWindow::event(QEvent*) () from /usr/lib/libkdeui.so.5
#39 0x00007f664209c174 in QApplicationPrivate::notify_helper(QObject*, QEvent*) () from /usr/lib/libQtGui.so.4
#40 0x00007f66420a0fe1 in QApplication::notify(QObject*, QEvent*) () from /usr/lib/libQtGui.so.4
#41 0x00007f6643c629c6 in KApplication::notify(QObject*, QEvent*) () from /usr/lib/libkdeui.so.5
#42 0x00007f6642edbbbc in QCoreApplication::notifyInternal(QObject*, QEvent*) () from /usr/lib/libQtCore.so.4
#43 0x00007f6642edef2f in QCoreApplicationPrivate::sendPostedEvents(QObject*, int, QThreadData*) () from /usr/lib/libQtCore.so.4
#44 0x00007f6642f06413 in ?? () from /usr/lib/libQtCore.so.4
#45 0x00007f663e99629d in g_main_context_dispatch () from /usr/lib/libglib-2.0.so.0
#46 0x00007f663e996a78 in ?? () from /usr/lib/libglib-2.0.so.0
#47 0x00007f663e996d09 in g_main_context_iteration () from /usr/lib/libglib-2.0.so.0
#48 0x00007f6642f06876 in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQtCore.so.4
#49 0x00007f664213f1be in ?? () from /usr/lib/libQtGui.so.4
#50 0x00007f6642edadb2 in QEventLoop::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQtCore.so.4
#51 0x00007f6642edafb7 in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQtCore.so.4
#52 0x00007f6642edf1ab in QCoreApplication::exec() () from /usr/lib/libQtCore.so.4
#53 0x00007f66315e5395 in kdemain () from /usr/lib/libkdeinit4_dolphin.so
#54 0x0000000000408002 in _start ()

-----Dolphin with preview disabled, closed and reopened with Preview not enabled-------
Application: Dolphin (kdeinit4), signal: Aborted
[Current thread is 1 (Thread 0x7f6644259760 (LWP 3489))]

Thread 3 (Thread 0x7f662a986700 (LWP 3491)):
#0 0x00007f6642b6dc24 in pthread_mutex_lock () from /lib/libpthread.so.0
#1 0x00007f663e996102 in g_main_context_dispatch () from /usr/lib/libglib-2.0.so.0
#2 0x00007f663e996a78 in ?? () from /usr/lib/libglib-2.0.so.0
#3 0x00007f663e996d09 in g_main_context_iteration () from /usr/lib/libglib-2.0.so.0
#4 0x00007f6642f068de in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQtCore.so.4
#5 0x00007f6642edadb2 in QEventLoop::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQtCore.so.4
#6 0x00007f6642edafb7 in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQtCore.so.4
#7 0x00007f6642df269f in QThread::exec() () from /usr/lib/libQtCore.so.4
#8 0x00007f6642ebdd8f in ?? () from /usr/lib/libQtCore.so.4
#9 0x00007f6642df50f5 in ?? () from /usr/lib/libQtCore.so.4
#10 0x00007f66366dfbc3 in ?? () from /usr/lib/libGL.so.1
#11 0x00007f6642b6bd40 in start_thread () from /lib/libpthread.so.0
#12 0x00007f664194eaed in clone () from /lib/libc.so.6
#13 0x0000000000000000 in ?? ()

Thread 2 (Thread 0x7f6629dd6700 (LWP 3501)):
[KCrash Handler]
#6 0x00007f66418b1705 in raise () from /lib/libc.so.6
#7 0x00007f66418b2b7b in abort () from /lib/libc.so.6
#8 0x00007f66418ea5a3 in ?? () from /lib/libc.so.6
#9 0x00007f66418f042a in ?? () from /lib/libc.so.6
#10 0x00007f66418f4666 in realloc () from /lib/libc.so.6
#11 0x00007f66366db451 in ?? () from /usr/lib/libGL.so.1
#12 0x00007f66366df93d in ?? () from /usr/lib/libGL.so.1
#13 0x00007f66366d9d95 in ?? () from /usr/lib/libGL.so.1
#14 0x00007f66440968fe in dl_open_worker () from /lib/ld-linux-x86-64.so.2
#15 0x00007f66440926d6 in _dl_catch_error () from /lib/ld-linux-x86-64.so.2
#16 0x00007f66440963da in _dl_open () from /lib/ld-linux-x86-64.so.2
#17 0x00007f663f695f26 in ?? () from /lib/libdl.so.2
#18 0x00007f66440926d6 in _dl_catch_error () from /lib/ld-linux-x86-64.so.2
#19 0x00007f663f6964cf in ?? () from /lib/libdl.so.2
#20 0x00007f663f695fc1 in dlopen () from /lib/libdl.so.2
#21 0x00007f663bb17b27 in ?? () from /usr/lib/libstreamanalyzer.so.0
#22 0x00007f663bb18336 in ?? () from /usr/lib/libstreamanalyzer.so.0
#23 0x00007f663bb400df in ?? () from /usr/lib/libstreamanalyzer.so.0
#24 0x00007f663bb402c1 in Strigi::StreamAnalyzer::StreamAnalyzer(Strigi::AnalyzerConfiguration&) () from /usr/lib/libstreamanalyzer.so.0
#25 0x00007f663c3dfb5d in ?? () from /usr/lib/libkio.so.5
#26 0x00007f663c3e0a47 in KFileMetaInfo::KFileMetaInfo(QString const&, QString const&, QFlags<KFileMetaInfo::What>) () from /usr/lib/libkio.so.5
#27 0x00007f663c4ae73c in ?? () from /usr/lib/libkio.so.5
#28 0x00007f6642df50f5 in ?? () from /usr/lib/libQtCore.so.4
#29 0x00007f66366dfbc3 in ?? () from /usr/lib/libGL.so.1
#30 0x00007f6642b6bd40 in start_thread () from /lib/libpthread.so.0
#31 0x00007f664194eaed in clone () from /lib/libc.so.6
#32 0x0000000000000000 in ?? ()

Thread 1 (Thread 0x7f6644259760 (LWP 3489)):
#0 0x00007f6642b6fa34 in pthread_cond_wait@@GLIBC_2.3.2 () from /lib/libpthread.so.0
#1 0x00007f6642df559b in QWaitCondition::wait(QMutex*, unsigned long) () from /usr/lib/libQtCore.so.4
#2 0x00007f6642df4e3c in QThread::wait(unsigned long) () from /usr/lib/libQtCore.so.4
#3 0x00007f6642eb1530 in QFileSystemWatcher::~QFileSystemWatcher() () from /usr/lib/libQtCore.so.4
#4 0x00007f6642eb1609 in QFileSystemWatcher::~QFileSystemWatcher() () from /usr/lib/libQtCore.so.4
#5 0x00007f6642eed6b5 in QObjectPrivate::deleteChildren() () from /usr/lib/libQtCore.so.4
#6 0x00007f6642ef2c89 in QObject::~QObject() () from /usr/lib/libQtCore.so.4
#7 0x00007f663b8bd459 in ?? () from /usr/lib/libsolid.so.4
#8 0x00007f66418b4221 in ?? () from /lib/libc.so.6
#9 0x00007f66418b42a5 in exit () from /lib/libc.so.6
#10 0x00007f6642107f28 in ?? () from /usr/lib/libQtGui.so.4
#11 0x00007f6643c60d98 in KApplication::xioErrhandler(_XDisplay*) () from /usr/lib/libkdeui.so.5
#12 0x00007f6643726fae in _XIOError () from /usr/lib/libX11.so.6
#13 0x00007f66437248ad in _XEventsQueued () from /usr/lib/libX11.so.6
#14 0x00007f664371522f in XEventsQueued () from /usr/lib/libX11.so.6
#15 0x00007f664213efec in ?? () from /usr/lib/libQtGui.so.4
#16 0x00007f663e995f24 in g_main_context_check () from /usr/lib/libglib-2.0.so.0
#17 0x00007f663e9967f2 in ?? () from /usr/lib/libglib-2.0.so.0
#18 0x00007f663e996d09 in g_main_context_iteration () from /usr/lib/libglib-2.0.so.0
#19 0x00007f6642f068de in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQtCore.so.4
#20 0x00007f664213f1be in ?? () from /usr/lib/libQtGui.so.4
#21 0x00007f6642edadb2 in QEventLoop::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQtCore.so.4
#22 0x00007f6642edafb7 in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQtCore.so.4
#23 0x00007f6642edf1ab in QCoreApplication::exec() () from /usr/lib/libQtCore.so.4
#24 0x00007f66315e5395 in kdemain () from /usr/lib/libkdeinit4_dolphin.so
#25 0x0000000000408002 in _start ()

New info! Now, it seems if I hover over another file (say a text file or document of any sort) BEFORE going to an .avi file, things work perfectly with Preview enabled. But, if I go *directly* to the .avi file soon as I'm in the directory (without hovering over any file first), it crashes reliably.

I guess you've to start with a clean kde config

Status? I cannot reproduce this.