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

[Jim]

i think it is very very unlikely that would ever happen.

hongyang wrote:
> thanks, Jim
>  
> I think that is to say the garbage data whould be not start with
> 
> $49 44 33 yy yy xx zz zz zz zz
> 
> is it true?
> 
> 
> 
> Jim 写道:
>> 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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>>
>>   
> 


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