ffmpeg + gcc 4.8.x dec_avcodec compatibility on win32

[totaam]

Issue migrated from trac ticket # 628

component: platforms | priority: major | resolution: wontfix | keywords: win32

2014-08-07 10:34:59: totaam created the issue

---

Despite compiling without warnings against both ffmpeg 2.3 and 2.3.1, the resulting dec_avcodec2 video decoder module causes cleanup errors on exit on win32. (that look like use after free or memory corruption: memory accesses at low addresses like 0x00000004)

I think it is safer to go with the 2.2.x branch (2.2.6 is out), even on OSX and Linux: done in r7175.
Please confirm that the problem exists with 2.3 on win32 and re-assign to me as non-blocker for 0.15.

[totaam]

2014-08-08 10:27:40: totaam commented

---

Note: may not be a bug, was seeing the same thing with 2.2.6, a good old reboot-windows later and it's gone..

Found some xpra cleanup bugs, fixed in r7199 (will backport).

[totaam]

2014-08-08 11:45:32: totaam commented

---

Well, well, well.

There is a problem, but it is not with the ffmpeg version.
I made a fresh 2.2.5 build (using the exact same command line) and it exhibits the same problem at runtime, the "old" 2.2.5 one does not.

Diffing the two trees shows absolutely nothing of interest, the only files shown as being different are the ".lib", ".a" and ".dll" - which is kind of expected.

So it must be a toolchain related bug. GCC got updated to 4.8.x in mingw32 recently (mingw-get update;mingw-get upgrade...).
It could be a bug in GCC or maybe the newer GCC turns on some stricter checks in the ffmpeg code.
Disabling w32threads makes no difference.

So, now we downgrade GCC back to 4.7, except the downgrade breaks mingw...
You have to download the few dlls that go MIA yourself from here: [http://sourceforge.net/projects/mingw/files/MinGW/Base/].
And miracle, it no longer crashes.

[totaam]

2014-08-08 12:18:30: totaam changed status from new to assigned

[totaam]

2014-08-08 12:18:30: totaam changed title from ffmpeg 2.3.x dec_avcodec compatibility to ffmpeg + gcc 4.8.x dec_avcodec compatibility on win32

[totaam]

2014-08-08 12:18:30: totaam changed priority from blocker to major

[totaam]

2014-08-08 12:18:30: totaam changed owner from smo to totaam

[totaam]

2014-08-08 12:18:30: totaam commented

---

(updating bug title)

[totaam]

2015-04-14 17:06:34: antoine commented

---

I don't have time for toolchain issues.

[totaam]

2016-01-23 05:51:51: antoine commented

---

FWIW: tried again today and it still causes crashes. Either building ffmpeg with gcc 4.8, or building the cython modules that link to it triggers crashes.

[totaam]

2016-09-27 10:07:21: antoine changed status from assigned to closed

[totaam]

2016-09-27 10:07:21: antoine set resolution to wontfix

[totaam]

2016-09-27 10:07:21: antoine commented

---

Superseded by #678.

Closing as wontfix: this build system will remain as it is for now, not updating gcc.