[ID3 Dev] APIC frame unsynchronization

Pyt py.thoulon at gmail.com
Thu Nov 24 08:01:02 PST 2005

Unsynch must be used only if you decide to.

In v2.3, there is a global unsynch bit that says whether the tag is unsync'd
or not. If this bit is set, all frames have to be unsync'd.

In v2.4, there is a bit per frame to specify whether a given frame is
unsync'd. If the bit is not set, you shall leave the FF's alone... :-)

Hope this helps,

On 11/23/05, Michal Vician <id3v2 at audiott.com> wrote:
> Hi guys.
> I have a problem and need advice:
> I've just written library which handles APIC frames. The writing process
> looks like this:
> 1. create an array of bytes which represents entire APIC frames
> 2. write the byte array to ID3v2 tag
> 3. if there is at least one FF Ex byte combination present use the
> unsynchonization scheme
> Is this correct?
> Now, why am I asking you this?:
> I've downloaded some applications which support APIC frame. As far as this
> applications are concerned they do not use unsynchronization scheme when
> writing the APIC frame - they are not able to show pictures written with
> my library.
> I'm just wondering why don't they use it?
> Is it just a bug on their side or am I wrong if I claim that
> unsynchronization must be used whenever the false sync bytes are found (FF
> Ex).
> Regards
> Miso
> --
> Michal Vician
> id3v2 at audiott.com
> http://www.audiott.com/
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