ID3v2.4 Footer

jeanmilost

Hello

I'm actually developping a class system to read/write into MP3's ID3v2.4 tags. I've found this description about footers on the site www.id3.org:

3.4. ID3v2.4 footer

To speed up the process of locating an ID3v2.4 tag when searching from the end of a file, a footer can be added to the tag. It is REQUIRED to add a footer to an appended tag, i.e. a tag located after all audio data. The footer is a copy of the header, but with a different identifier.

ID3v2 identifier "3DI"
ID3v2 version $04 00
ID3v2 flags %abcd0000
ID3v2 size 4 * %0xxxxxxx

The ID3v2.4 footer is marked as optional, but here it's seems that into some cases, this footer is required. So, this description is not easy to understand. My questions are :
- Is ID3v2.4 footers are optional or required ?
- If optionals, in whitch cases there are required ?

Thx, regards...

PCForrest

: Hello
:
: I'm actually developping a class system to read/write into MP3's
: ID3v2.4 tags. I've found this description about footers on the site
: www.id3.org:
:
: 3.4. ID3v2.4 footer
:
: To speed up the process of locating an ID3v2.4 tag when searching
: from the end of a file, a footer can be added to the tag. It is
: REQUIRED to add a footer to an appended tag, i.e. a tag located
: after all audio data. The footer is a copy of the header, but with a
: different identifier.
:
: ID3v2 identifier "3DI"
: ID3v2 version $04 00
: ID3v2 flags %abcd0000
: ID3v2 size 4 * %0xxxxxxx
:
: The ID3v2.4 footer is marked as optional, but here it's seems that
: into some cases, this footer is required. So, this description is
: not easy to understand. My questions are :
: - Is ID3v2.4 footers are optional or required ?
: - If optionals, in whitch cases there are required ?
:
: Thx, regards...
:

For prefixed tags (before the audio stream), you don't need to include either a footer or padding. So in this context they are considered OPTIONAL.

If you choose to include a footer there must be no padding. In other words they are mutually exclusive. You can have one or the other, but you MUST NOT include both.

However, a footer MUST be present when a tag is postfixed (after the audio stream). In this context it is REQUIRED. Since they are mutually exclusive, it therefore follows that padding MUST NOT be included in a postfixed tag.