This plugin uses the MP4v2 library to play mp4/m4a files.
It is limited to file_decode.

They are only used inside dsdiff_read_metadata_extra().

Failure to read another chunk header is not fatal.  Continue to read
metadata.

Move code from the FAAD decoder plugin.

This loop is completely unnecessary.  We just need to find the first
ADTS frame and feed it into NeAACDecInit().

Eliminate duplicate cleanup code.

Previously, MPD tried to slurp the whole song file, count the number
of frames and calculate the song duration from that.  That however is
extremely expensive for remote files, and will delay playback for a
long time.  Workaround: check only the first 128 frames and try to
extrapolate from here.  Fixes Mantis ticket 0004035.

Eliminate more duplicate code.

Don't bother to check for ADIF just because the stream is not
seekable.

Merge some duplicate code.

Eliminate some overhead when the caller doesn't need the buffer.

Checking the integer is faster, easier and more reliable.

.. instead of declaring a new constant.

Replaces the loop in sndfile_vio_read(), eliminating duplicate and
fragile code.

.. instead of InputStream::LockRead(). The former is cancellable.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>