Find ffmpeg in frozen applications

When this lib is included in a frozen application, the ffmpeg executable must be shipped along too. We should:

• Perhaps provide a simple function that can be used in the freeze script to copy the ffmpeg exe.
• Make get_ffmpeg_exe() look in the frozen application directory.

While we don’t have this, please copy the ffmpeg executable yourself, and use the IMAGEIO_FFMPEG_EXE environment variable to point to it.

[paulmueller]

It also works on linux. I think this one can be closed.

[almarklein]

Thanks for the confirmation, we can close!