Pack opencv_ffmpeg310.dll

[techtonik]

Build process downloads ffmpeg .dll, but fails to pack it into resulting wheel.

opencv/opencv#6803

[skvark]

If there's no licensing related issues, it can be added to the wheel.

[techtonik]

I am not aware of any. Sources are available, so all GPL requirements are met.

[virtuald]

If it's GPL, that would be a problem for non-GPL projects if they didn't realize what they were using (as OpenCV is not GPL, so they normally wouldn't need to worry about that).

[skvark]

I'm going to leave this issue open for now. I'm not a lawyer so I'm not sure what consequences there are if the GPL licensed ffmpeg binary is distributed within this package.

[techtonik]

@skvark ask at https://opensource.stackexchange.com

[takluyver]

I'm not a lawyer either, but my understanding is that it would be OK to distribute a GPL component with OpenCV, but the whole package would then fall under the GPL, along with anything that uses it.

However, FFmpeg itself is LGPL, with optional GPL parts. If it is compiled without the --enable-gpl flag, the GPL should not apply, so it should be sufficient to include an appropriate copyright notice for FFmpeg and a copy of the LGPL document.

https://ffmpeg.org/legal.html

[skvark]

I think you are correct. On Windows this is easy to fix because the FFmpeg dlls are precompiled as LGPL (https://github.com/opencv/opencv/tree/master/3rdparty/ffmpeg) and can be easily copied to the wheel package during build. I guess that on OS X the situation is probably similar to Windows. On Linux it gets more complicated since FFmpeg has to be compiled separately as LGPL on the manylinux containers. However, it should not be a problem but requires some work.

I'll start working on this FFmpeg issue. Contributions are more than welcome. In the meantime, non-video features of the opencv-python wheels should work just fine.

[takluyver]

Thanks @techtonik and @skvark for the fix! Any chance of a new release on PyPI? @cachitas is making an example of bundling it into a windows installer (takluyver/pynsist#79), which should work neatly once the new wheel is available.

[skvark]

I can make the release. However, OS X / Linux builds are still missing ffmpeg support since it's a bit more complicated to enable it on them (especially on Linux due to the Cent OS 5 manylinux containers).

[takluyver]

For our example, it's only the Windows build that is necessary, so if it's easy to do a release, I wouldn't wait for a solution for the other platforms.

I've managed to get pygame plus its dependencies built and bundled in a manylinux container, though there were no license concerns to watch out for there. It was mostly a matter of compiling new versions of the dependencies from source to avoid the ancient versions available in CentOS 5's repos. http://www.pkgsrc.org/ might help there; I didn't know about it at the time.

[skvark]

Good to know. I'll make now the release.