Fix some warnings

[ebachard]

Hello,

Playing with your lib, I fixed some warnings, because ffmpeg is always changing.
Just 2 warnings remain (codec is deprecated), but I can't fix them easely, since the API depends on that.

Just in case you are interested with a part or the full diff, you can use LGPL (like the one in your code). Feel free to ask me if there is a problem.

Thanks again for sharing your code

--
ericb

aveasy_fixed_warnings_ericb.txt