* [http://age.hobba.nl/audio/mirroredpages/ogg-tagging.html Ogg Vorbis Comment Field Recommendations]
* [http://gophernet.org/articles/vorbiscomment/ Proposals for extending Ogg Vorbis comments]
Comments are intended to be free-form, but for the purposes of interoperability, it is helpful to define tag sets for particular applications, and provide some guidelines for machine parsing. Note that some field names have to be non-free-form to achieve machine parsing.
==== METADATA_BLOCK_PICTURE ====
The [http://flac.sourceforge.net/format.html#metadata_block_picture binary FLAC picture structure] is base64 encoded and placed within a
vorbis comment with the tag name "METADATA_BLOCK_PICTURE". This is the preferred and recommended way of embedding cover art within vorbis comments. It has the following benefits:
* Easy to use for developers since the identical (or similar) structure is also used by FLAC and MP3.
* Multiple image blocks MAY be included as separate METADATA_BLOCK_PICTURE comments.
* There may only be one each of picture type (APIC type) 1 and 2 in a Vorbis stream.
* Block order is significant for some types and applications should preserve the comment order when reading or writing
Vorbis comment headers. The block order may be used to determine the order pictures are presented to the user.
===== Playback tests =====
* XMPlay 3.4.2: no problem
* Nero ShowTime: no problem
'''Tested hardware players'''
* Logitech Squeezebox:
doesn't play this file ( and all other oggs with embedded picture) ** Workaround: The needed Server Software (called SqueezeCenter) can convert ogg to mp3 on the fly, and has also no problem to convert oggs with embedded pictures
* Sandisk Sansa Fuze (Firmware 01.01.22): Hangs up when trying to playback the demo file - had to reset the player
** Note: The "Fuze" can play ogg vorbis files which have embedded pictures from "Easytag"
* Cowon D2: no problem (latest Firmware: 2.59, 8GB Version)
* iRiver E100: no problem (latest Firmware: 1.16 G_U, 8GB Version)
'''Tested tag editors'''
* Easytag 2.1.6: can open the file to edit the normal tag fields
* MP3Tag 2.42e: can open the file to edit the normal tag fields
'''Tested other software'''
* Total Recorder:
can open the file without a problem.
==== Unofficial COVERART field (deprecated) ====
* the cover art can't be linked
* the base64 string is displayed within many tag editors as plain text because of their missing support for this "COVERART" field
* it may breaks the playback on hardware players because of a large
vorbis comment headerThe unofficial "COVERART" field is supported for example by such software as AudioShell (http://www.softpointer.com/AudioShell.htm) and Total Recorder (http://www.totalrecorder.com/).
===== Conversion to METADATA_BLOCK_PICTURE =====
* Encode the new picture block, remove the COVERART tag from the comments and add the METADATA_BLOCK_PICTURE entry.
* If multiple tags are being converted the order of the METADATA_BLOCK_PICTURE tags should be the same as that of the COVERART tags they are replacing.
=== Date and time ===
==== ISO proposal ====
The date format for any field describing a date must follow the ISO
scheme: YYYY-MM-DD, shortened to just YYYY-MM or simply YYYY.
We have been recommending this usage with the DATE tag for some time. It is proposed that the spec be amended to include this information for machinability.
==== Proposal: Inclusion of URL in ENCODER value ====
The encoder field name must be a unique URL providing both encoder software name and version. If no unique URL address is available were both name and version is available; then the version number can be specified by separating with a space character. For example:
The ''Dublin Core Metadata Initiative'' recommends the use of ‘rights’ to describe license and copyright matters. The web feed format Atom 1.0 has implemented a rights element in their specification.
==== Improving existing fields proposal ====
Similar to the DATE tag above, we have generally recommended that a URL uniquely identifying the license be included in the LICENSE field to allow machine identification of the license. This is in agreement with the proposal in the Creative Commons wiki. Since the COPYRIGHT field is a human-readable statement of the copyright, like the proposed RIGHTS tag above, some people include a license url there. Therefore if a url can't be found in a LICENSE tag if any, applications should use one from the COPYRIGHT tag, if any. Contact information for verification, attribution, relicensing, etc. can be obtained from the COPYRIGHT field, but Creative Commons also recommend a separate CONTACT tag for this information. This is reasonable, so we propose it be included.
=== Geo Location fields ===
The LOCATION field is meant to carry a human readable location for the recording/creation of the media file.
Having geographical coordinates according to [http://en.wikipedia.org/wiki/World_Geodetic_System WGS84] can be useful as well, especially in a form that can be machine parsed. The agreed format is similar to this [http://en.wikipedia.org/wiki/Geo_(microformat) geo microformat]:
See http://www.replaygain.org/ for detailed information about Replay Gain and how the different values are calculated.
== Implementations ==
* [http://sbooth.org/importers/ Spotlight
importer]* vorbiscomment* [http://www.xiph.org/oggz/ oggz-comment]