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

svn r13289 of libvorbis introduced static callbacks (like OV_CALLBACKS_DEFAULT)
defined in "vorbisfile.h" header. First released version with this change is libvorbis-1.2.2.
In libversion-1.2.3 OV_EXCLUDE_STATIC_CALLBACKS define was added to avoid
warnings about unused static callbacks. Information on the OV_EXCLUDE_STATIC_CALLBACKS
can be found in http://svn.xiph.org/trunk/vorbis/CHANGES.

Don't initialize "vc" and "cs" with FLAC__metadata_object_new(); that
value is overwritten by FLAC__metadata_get_tags() and
FLAC__metadata_get_cuesheet().

The "off_t" type may change when you enable or disable large file
support on 32 bit platforms.  This caused severe ABI problems within
MPD when we enabled LFS for the first time: two sources included
config.h and sys/types.h in different order, and had different off_t
sizes - leading to memory corruption because of ABI incompatibility.
This patch attempts to get rid of all public "off_t" uses: it removes
"off_t" from the input_stream ABI/API, and switches to GLib's 64 bit
"goffset" type.  This may hurt 32 bit embedded platforms a tiny bit,
but that's not even measurable.

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".

When the ID3 tag in an AAC file is larger than the current buffer, the
function decoder_buffer_consume() aborts.  By using the new function
decoder_buffer_skip() instead, we can safely skip the ID3 tag.

When parsing the songlength database fails, the code forgot to free
the memory allocated by the raw file data.

The caller is responsible fro freeing GError objects.  That
g_error_free() call was missing in two places.

The error handler dereferences GError*, but did not retrieve that
object from g_file_get_contents().

This patch made ov_time_total() unusable, and MPD did not know the
duration of songs.

[mk: added autoconf test; fixed songlen_data_size type]

Still missing:
- seeking
- tags
- streaming
- encodings other than MPG123_ENC_SIGNED_16

fopen change for win32 in tag dup of vorbis
win32 adaption for head changes

using ov_test_callback with function CALLBACKS_STREAMONLY will cause
scanning to stop after the comment field.  ov_open (and ov_test)
default to CALLBACKS_DEFAULT which scans the file structure causing a
huge slowdown.  The speed improvement is huge: It scanned my files
around 10x faster This procedure has been recommended by monthy (main
vorbis developer) and was said to be safe for scanning files.

The function flac_cue_track() first calls FLAC__metadata_object_new(),
then overwrites this pointer with FLAC__metadata_get_cuesheet().  This
allocate two FLAC__StreamMetadata objects, but the first pointer is
lost, and never freed.

The FLAC replaygain parser used the "||" operator.  This made the code
stop after the first value which was found.

When one metadata check fails, return quickly.  This removes 2 levels
of indent.

This belongs into "git annotate" or AUTHORS.

When libid3tag is disabled, the libmad decoder plugin is unable to
identify ID3 frames.  If the file starts with an (unidentified) ID3
frame, it assumes that the file is not a valid MP3 song.  This patch
solves this by adding minimal stubs for the ID3 functions.

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.

External cue sheet file for "file.flac" should be named as "file.flac.cue".

Initialize flac_data.tag right after flac_data_init().  This way, the
"goto fail" won't jump to the point where tag_free(NULL) can be
called.

Call av_metadata_get() in a loop.

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

strcasecmp() is locale dependent, making it a bad choice for internal
string comparisons.

strcasecmp() is locale dependent, making it a bad choice for internal
string comparisons.

Move the declaration of "i" into the "for" loop.