What JACK expects is already implemented in MPD, just not used.  The
sample format conversion code in the JACK plugin was redundant and
could reduce sound quality.

Here's a change to dynamically allocate the DSD ID3 tag buffer.
Pretty much anything with cover art is going to exceed the existing,
static 4k limit...  Here's a change to dynamically allocate the buffer
and sanity check it at some upper limit.  I rather arbitrarily pulled
256k out of thin air just to keep a corrupt file from causing it to
trying to allocate a buffer larger than available memory.

Make sure that the log callback is installed.

Use the duration of the stream we're actually decoding - not the
"global" attribute AVFormatContext::duration which may differ.