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This table shows what tag types are supported for which audio formats. Formats for which no metadata support is present are omitted.
| ID3v1 | ID3v2 | APE | Ogg Xiph Comments | FLAC Pictures | Musepack ReplayGain | Generic StreamMeta | MPEG StreamMeta | Module info | |
| FLAC | R/W | R/W | |||||||
| Ogg Vorbis | R/W | ||||||||
| Ogg Vorbis (stream) | R | R | |||||||
| MPEG Audio | R/W | R/W | R/W | ||||||
| MPEG Audio (stream) | R | R | |||||||
| MOD Audio | R | ||||||||
| Musepack | R/W | R | |||||||
| Monkey's Audio | R/W | ||||||||
| WavPack | R/W |
ID3v1 and ID3v1.1 (http://www.id3.org/ID3v1) are fully supported. The difference between the two is the presence or absence of a separate Track Number field, which was added in ID3v1.1. Aqualung automatically parses the tag choosing the right version. When writing the tag, it is written as ID3v1.1 if a Track Number frame is present, and written as ID3v1 otherwise.
The Genre field has a fixed set of possible contents in ID3v1 and ID3v1.1. This is enforced by a drop-down menu in the metadata editor GUI.
ID3v2 tags are supported with the restriction that the tag MUST be at the beginning of the file. Tag versions before ID3v2.3 are considered obsolete and not supported. Support for ID3v2.3 tags (http://id3.org/id3v2.3.0) is read-only, meaning that they are parsed, but converted to ID3v2.4 whenever saved back to file. ID3v2.4 tags (http://id3.org/id3v2.4.0-structure) are supported in both read and write mode.
ID3v2.4 tags are always written using UTF-8 as the string encoding of non-ASCII text data, and unconditionally employing unsynchronisation on all frames. Extended headers are neither parsed nor written. Padding is added when creating a new file (via CD ripping or file export) or rewriting a tag that does not fit in its earlier space (e.g. when adding a picture frame, which is usually larger than the remaining padding, thus mandating the re-writing of the whole file). In these cases the policy for determining the amount of padding is that the size of the tag should be an integer multiple of 2K, and the added padding should be between 2K and 4K.
Not every frame defined by the ID3v2 standards is implemented; however, the commonly used subset of the frames is available. In particular, all text information frames (T***) including `User defined text frame' (TXXX), URL link frames (W***) including `User defined URL link frame' (WXXX), comments (COMM), relative volume adjustment 2 (RVA2), and attached picture (APIC) frames are supported.
Some ID3v2.3 frames that have been discontinued in ID3v2.4 are supported by reading and converting them to other (functionally equivalent) frames: TDAT, TIME, TRDA and TYER are treated as TDRC and TORY is treated as TDOR.
Note that the RVAD frame in ID3v2.3 is not supported.
APEv1 and APEv2 tags are supported with the restriction that the tag MUST be located at the end of the file, possibly before an ID3v1 tag. Standard items are supported as well as ReplayGain-related frames, and picture frames which are by convention binary items identified by a key starting with `Cover Art' followed by the picture type definition in brackets. This is compatible with most existing tagging software.
Ogg Xiph comments (also known as Ogg Vorbis comments) are supported according to the recommended field names in the Vorbis format spec. In addition to this, COMMENT, DISC, and ReplayGain-related fields are also supported.
In FLAC files there may be an Ogg Xiph comment block along with separate picture blocks that contain one embedded picture each. This tag is Aqualung's pseudo-tag for referring to the set of picture blocks in a FLAC file, so the only frame you can add to this tag is the `Attached picture'.
In Musepack SV7 streams there may be ReplayGain data in the file (not in a metadata tag, but in the coded audio data itself). Technically, it is always present, but is only treated as existent when it is nonzero. Aqualung displays (and has the capability to use) this information by referring to it as a `Musepack ReplayGain' pseudo-tag (which, again, is not a proper metadata tag in reality). This information is read-only.
This is a read-only pseudo-tag carrying information that was obtained when speaking to the Icecast or SHOUTcast stream server. Specifically, the relevant HTTP header fields received from the server are saved in this pseudo-tag and made available for viewing. These currently include the `Icy-Name', `Icy-Description' and `Icy-Genre' fields.
This is a read-only pseudo-tag carrying information that was received while listening to an MPEG stream on internet radio via SHOUTcast. This information consists of `key:value' pairs, and is thus fairly similar to Ogg Xiph comments. Usually internet broadcast stations include only a small number of fields, but since the field name is included in the transmission, there is no restriction on the supported fields.
For files handled by the MOD library, some read-only information about the file (number of channels, instruments, etc.) is displayed.
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