for update ffmpeg. delete old one.
Squashed 'captive/ffmpeg/csrc/' content from commit 9ba6b17

git-subtree-dir: captive/ffmpeg/csrc
git-subtree-split: 9ba6b17add28b57c7e0be2b43df50d104c043be0
Merge commit '58ff4b1bf0e4099c8d8a6176d9cc5f4b8338497c' as 'captive/ffmpeg/csrc'