This patch prepares support for floating point samples (and probably
other formats).  It changes the meaning of the "bits" attribute from a
bit count to a symbolic value.

The plugin code tried to force libavcodec to supply stereo samples.
That however has never actually worked.  By removing this code, we are
able to play surround files for the first time.

On some platforms, libavcodec wants the output buffer aligned to 16
bytes (because it uses SSE/Altivec internally).  It will segfault when
you don't obey this rule.

Let the audio_check library verify the audio format in all (relevant,
i.e. non-hardcoded) plugins.

After we've been hit by Large File Support problems several times in
the past week (which only occur on 32 bit platforms, which I don't
have), this is yet another attempt to fix the issue.

libavformat gives us the song artist in the "author" field.  Since we
use av_metadata_conv(), we don't need to check for "artist".

Convert the metadata with the libavformat function av_metadata_conv().
This ensures that canonical tag names are provided by libavformat, and
we can remove the "artist" vs "author" workaround.

Usually, we read our "artist" tag from ffmpeg's "author" tag.  In some
cases however (e.g. APE), this tag is named "artist".  This patch
implements a fallback: if no "author" is found, MPD tries to use
"artist".

It makes no difference right now, but we're about to add an endianness
flag and will want to make sure it's correctly initialised every time.

Call av_metadata_get() in a loop.

This warning is useless.  I assume the author added it for debugging
purposes.

This updates the copyright header to all be the same, which is
pretty much an update of where to mail request for a copy of the GPL
and the years of the MPD project. This also puts all committers under
'The Music Player Project' umbrella. These entries should go
individually in the AUTHORS file, for consistancy.

function was implemented in the version we are comparing to so there must be higher or equal

After much research[1][2][3] this should be the majority of currently
supported file extensions and mime-types for the currently supported
ffmpeg formats. This list maybe incomplete, but it's more complete
than anything else out there that I've been able to find. This list
needs to be updated every now and again as the ffmpeg sources support
more formats.

 1. Sources
 2. wiki.multimedia.cx
 3. filext.com

Preparing for per-plugin configuration sections in mpd.conf.

The ffmpeg library supports the "True Audio Codec".  The entry in
ffmpeg_suffixes was missing.

The "current" variable is used for calculating the seek destination,
and was declared as "int".  With very long song files, the 32 bit
integer can overflow.  ffmpeg expects an int64_t, which is very
unlikely to overflow.  Switch to int64_t.

When ffmpeg cannot estimate the elapsed time, it sets
AVPacket.pts=AV_NOPTS_VALUE.  Our ffmpeg decoder plugin did not check
for that special value.

If avcodec_decode_audio2() returns no output for an AVPacket,
libavcodec may buffer some data, and return a larger chunk of output
later.  This patch disables a lot of bogus warnings.

Output the name of the codec as a debug message.  During my tests,
ffmpeg never filled this struct member, but it may do so in the past,
and this debug message might become helpful.

ffmpeg_tag_internal() does not look for a few tags that mpd
supports. Most noteably:

 comment -> TAG_ITEM_COMMENT -> Description
 genre -> TAG_ITEM_GENRE -> WM/Genre (not WM/GenreID)
 year -> TAG_ITEM_DATE -> WM/Year

I *think* that this is the last of the tags that AVFormatContext() in
ffmpeg supports that mpd also uses.

Use GLib's G_GNUC_UNUSED instead of gcc.h's mpd_unused.

The old code casted it to a 32 bit integer, which cut off bits.
AVFormatContext.duration is a int64_t, so use this type.

Use NULL instead.  Found by sparse.

Refuse to play audio formats which are not supported by MPD.

The ffmpeg library provides some of the song metadata in the
AVFormatContext struct.  Pass it from there to MPD.

With whence==AVSEEK_SIZE, the seek function should return the file
size, not the current offset.  Check the return value of
input_stream_seek().

The stream_decode() and file_decode() methods returned a boolean,
indicating whether they were able to decode the song.  This is
redundant, since we already know that: if decoder_initialized() has
been called (and dc.state==DECODE), the plugin succeeded.  Change both
methods to return void.

Instead of having a seprate try_decode() method, let the
stream_decode() and file_decode() methods decide whether they are able
to decode the song.