This loader supports whatever format libavformat and libavcodec can
handle. Currently only seekable streams are supported, and we still have
some limitations as to the number of channels and sample format.
Plays all non-streaming audio files at:
https://tools.woolyss.com/html5-audio-video-tester/
Rather than checking the avcodec version in CMake, check it using the
avcodec version macros in the only source file that needs to know about
the AVFrame API/ABI change in version 59.24.100. This is friendlier to
other build systems that would rather avoid configure time checks.
