Test builds against ffmpeg 2.3.3

[rzurad]

Make sure test suite behaves as expected when built with ffmpeg 2.3.3:

• libavcodec 55.69.100
• libavutil 52.92.100
• libavformat 55.48.100

[rzurad]

Commit 1ae241484 (in master) fixes compiler errors with ffmpeg 3.x, but it's at the expense of no longer supporting compiling against ffmpeg 2.

Keeping this ticket open until there's directives that allows it to compile against both.

(hmm, I opened it almost 2 years ago... at this rate, I'll actually fix it 2 years from now... See you then!)