Require libavcodec >= 57.37

In ffmpeg/doc/APIchanges:

> 2016-04-21 - 7fc329e - lavc 57.37.100 - avcodec.h
>   Add a new audio/video encoding and decoding API with decoupled input
>   and output -- avcodec_send_packet(), avcodec_receive_frame(),
>   avcodec_send_frame() and avcodec_receive_packet().

Refs de9b79e

Refs #2862 <#2862>

app/meson.build

@@ -85,7 +85,7 @@ if not get_option('crossbuild_windows')
     # native build
     dependencies = [
         dependency('libavformat', version: '>= 57.33'),
-        dependency('libavcodec'),
+        dependency('libavcodec', version: '>= 57.37'),
         dependency('libavutil'),
         dependency('sdl2', version: '>= 2.0.5'),
     ]