[ID3 Dev] How do you know ID3 v1 without ID3v2

[Jim]

If the header for the tag was properly written, you can check it using
the pattern that Jud gave before:

An ID3v2 tag can be detected with the following pattern:
$49 44 33 yy yy xx zz zz zz zz
Where yy is less than $FF, xx is the 'flags' byte and zz is less than $80.


So, if the first 3 characters are "ID3", then check that the next two
(yy) are less than $FF and that the last four (zz) are less than $80.



hongyang wrote:
> Yes, you have my idea.
> 
> I am also confused about that.
> 
> garbage data would be start like "00 00 00 00 "chars and so on some "sync"
>  pattern. but I am not confirm this.
> 
> 
> Jim 写道:
>> I might be confused but I think what he is asking is if a MP3 file that
>> does not have an ID3v2 tag could somehow start with the characters "ID3".
>>
>> Or another way to say it is could there be "ID3" at the start of a MP3
>> file but it is not a ID3v2 tag?
>>
>> I don't think this would happen but I also think that garbage data can
>> sometimes appear at the beginning of an MP3 file.  So I don't think it
>> is impossible.  I think that's why some players search for a certain
>> "sync" pattern to identify the start of the real data.  Can someone
>> confirm this?  (Or am I completely off on this?)
>>
>> Jim
>>
>>
>>
>>
>> Jud White wrote:
>>   
>>> No, frame headers would never start with ID3.
>>>
>>> hongyang wrote:
>>>     
>>>> Thanks,
>>>>
>>>> I think maybe you misunderstand me, I mean whether the situation could
>>>> happen, the MP3 music media data(not the Tag frame data) start with
>>>> "ID3", but this "ID3" is not the ID3v2 Tag's identifier.
>>>>
>>>> In fact the MP3 file without ID3v2 Tags, only ID3v1 exist.
>>>>
>>>> do you think this situation would like happen.
>>>>
>>>> thank u again...
>>>>
>>>> Jud White 写道:
>>>>       
>>>>> An ID3v2 tag can be detected with the following pattern:
>>>>> $49 44 33 yy yy xx zz zz zz zz
>>>>> Where yy is less than $FF, xx is the 'flags' byte and zz is less than $80.
>>>>>
>>>>> http://id3.org/id3v2.3.0#head-697d09c50ed7fa96fb66c6b0a9d93585e2652b0b
>>>>>
>>>>>
>>>>> hongyang wrote:
>>>>>   
>>>>>         
>>>>>> Hello everyone,
>>>>>>
>>>>>> I have a quesetion, if I know the .mp3 file has ID3v1 Tag, and I am not
>>>>>> sure whether it also has ID3v2 Tag.Now whether the condition would happend
>>>>>> that the start of media data are "ID3" ,but the "ID3" is not the
>>>>>> identifier of ID3v2.
>>>>>>
>>>>>> My english is very poor,so please forgave me.
>>>>>>
>>>>>> Thank you all.
>>>>>>
>>>>>> hongyang
>>>>>>
>>>>>>
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>>>>>>
>>>>>>   
>>>>>>     
>>>>>>           
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>>>>>
>>>>>   
>>>>>         
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>>>
>>>
>>>     
>>
>>
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>>
>>   
> 


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