if I use the sound test  file as my default file (replacing it into .blender/.B25.blend or using Ctrl+U after opening it) crashes Blender at init time.
It crashes at line 191 in file: //intern/audaspace/ffmpeg/AUD_FFMPEGReader.cpp
>> [ if(av_open_input_stream(&m_formatCtx, m_byteiocontext, "", fmt, NULL)!=0) AUD_THROW(AUD_ERROR_FILE); ]
The file works fine if I load it. The only problem is when this is the Blender intial file.
CMake build with FFMpeg, OpenAL, SND_FILE and SDL and without Jack and QuickTime
Scons build with FFMpeg, OpenAL and SDL and without SND_FILE, Jack and QuickTime
 - https://svn.blender.org/svnroot/bf-blender/trunk/lib/tests/sound/main.blend
I currently have a blender source, etc. here and can only have a closer look later.
Does the crash happen in av_open_input_stream or due to the thrown exception?
I guess the first, because the exception normally would get caught. So the reason might be, that the packedfile data is not loaded when this function is called and the application crashes due to an access violation. So this would be the direction to further investigate on.
Is there any difference between the .B25.blend files created with those two methods? "(replacing it into .blender/.B25.blend or using Ctrl+U after opening
There should be, as the later also saves the Preferences into the file. Only replacing it with the original it won't have Preferences in it.
1) It crashes in the if(av_open_input_stream(&m_formatCtx, m_byteiocontext, "", fmt, NULL)!=0) line, not in the next line.
2) It crashes with the unpacked file too
3) There shouldn't be any big difference between replacing the .B25.blend file and Ctr+U, at least none relative to this bug