Merci Beaucoup pour ton aide.
I did have some Youtube video files in there. There's probably something in those files that's troublesome. For now I just took them out. But I'll investigate this.
Here's a crash log: Those first lines about reaper_video.dylib are ALWAYS there.
Exception Type: EXC_BAD_ACCESS. (SIGSEGV)
Thread 0 Crashed:: Dispatch queue: com.apple.main-thread
0 reaper_video.dylib 0x000000011805243b SHM_MsgReplyConnection::RunInternal(int, SHM_MsgReplyConnection::WaitingMessage**) + 123
1 reaper_video.dylib 0x0000000118053323 SHM_MsgReplyConnection::Send(int, void const*, int, void*, int, int const*, void const*, int, WDL_HeapBuf*) + 2003
2 reaper_video.dylib 0x000000011804deee createBridgeDecoder(char const*, int, Decoder**) + 1102
3 reaper_video.dylib 0x0000000117f563bf PCM_source_dshow:
pen_decoders(char const*, Decoder**, Decoder**) + 1279
4 reaper_video.dylib 0x0000000117f798cd PCM_source_dshow::Open(char const*, int) + 1213
5 reaper_video.dylib 0x0000000117f7bf2a PCM_source_dshow::LoadState(char const*, ProjectStateContext*) + 2522
6 com.cockos.reaper 0x000000010012d62d MediaItem::LoadState(char const*, ProjectStateContext*) + 14381
7 com.cockos.reaper 0x00000001001fceee MediaTrack::LoadState(char const*, ProjectStateContext*, int, int, WDL_PtrList<MediaTrack>*, bool, bool) + 15918
8 com.cockos.reaper 0x000000010014077d do_load(ReaProject*, ProjectStateContext*, int) + 16653
9 com.cockos.reaper 0x0000000100149c2e LoadProjectFromContext(ReaProject*, ProjectStateContext*, char const*, int) + 766
10 com.cockos.reaper 0x00000001001488ec LoadProject(ReaProject*, char const*, int*, int) + 972
11 com.cockos.reaper 0x00000001000af3b9 DoProjectLoad(char const*, bool, int) + 537
12 com.cockos.reaper 0x00000001000ad0dd Main_openProject(char const*) + 509
13 reaper_sws_extension.dylib 0x000000011c346781 OpenProjectsFromList(COMMAND_T*) + 481
14 reaper_sws_extension.dylib 0x000000011c29a2ab hookCommandProc(int, int) + 731
15 com.cockos.reaper 0x000000010006e828 Main_OnCommandEx2(int, int, ReaProject*) + 120
16 com.cockos.reaper 0x00000001000d3f2f Main_OnCommandEx(int, int, ReaProject*) + 31
17 com.cockos.reaper 0x000000010035fdbb KBD_OnMainActionEx(int, int, int, int, HWND__*, ReaProject*) + 187
18 com.cockos.reaper 0x000000010035fcec KBD_OnMainAction(int, int, int, int, HWND__*) + 12
19 com.cockos.reaper 0x0000000100367b7f kbd_onAction(KbdAccel*, int, int, int, bool, KbdSectionInfo*, HWND__*) + 543
20 com.cockos.reaper 0x00000001003678ce kbd_translateAccelerator(HWND__*, MSG*, KbdSectionInfo*) + 462
21 com.cockos.reaper 0x000000010036c43f -[REAPERapp sendEvent:] + 3167
22 com.apple.AppKit 0x00007fff93a9bdf2 -[NSApplication run] + 796
23 com.apple.AppKit 0x00007fff93a65368 NSApplicationMain + 1176
24 com.cockos.reaper 0x0000000100010d1c main + 28
25 com.cockos.reaper 0x0000000100010ce4 start + 52