[ID3 Dev] First byte of the first frame: the inevitable byte (revised)

[Mitchell S. Honnert]

If all you want to do is find the first audio frame, you don't necessarily
need to know the ID3v2 tag length.  (If you do need the length, it's clearly
spelled out in the spec.)  Do a search on MPEG header and you'll find the
byte pattern which identifies the start of an audio frame.  One location for
this information is at http://www.mp3-tech.org/ in the Programmer's Corner
section.  (In writing my .NET tag editor library, I decided to add support
for MPEG data like bit rate and frequency, and this is the page I used as a
reference.)

 

Mitchell S. Honnert

www.UltraID3Lib.com

 

 

  _____  

From: Silas Pradetto [mailto:silas at sonoroussound.com] 
Sent: Wednesday, January 25, 2006 2:22 PM
To: id3v2 at id3.org
Subject: [ID3 Dev] First byte of the first frame: the inevitable byte
(revised)

 


thanks, the files encoded by different encoders I would consider to be
different, i only want to detect files that i may have downloaded twice and
are in different dirs, and someone may have changed the tag on one not the
other, but the file is the same otherwise. thanks for the suggestion on the
already-done dup remover, as i have no real time for writing this stuff
anymore, the other question is how to find the length of the ID3v2 tag???

thanks again,

silas


 

If you really want to reinvent the wheel you can -- you have to determine
how long the ID3v2 tag is, skip that, then read the rest of the file
(excepting the last 256 bytes if it has an ID3V1 tag). How you do this
depends entirely on the library (if any) you use. Note that if all you do is
a byte-by-byte comparison then you still won't detect dupes if the files
were encoded by different encoders, or at different bitrates, or various
other issues. 

If you don't want to reinvent the wheel, then go take a look at
musicbrainz.org -- they've already done this. And taken care of the various
issues I listed above.

On 1/25/06, Silas Pradetto <silas at sonoroussound.com> wrote:

I recently became added to this system of emails, and I am trying to write a
program to find duplicates in MP3's. I wish to only take into consideration
the actual song data, not bytes of any tags. Therefore, how do I find the
first byte in the file of actual song data, ie the first byte of the first
frame? I want to be able to detect duplicates that have different tags but
are the exact same audio information. Also, to make the program faster, I
would like to know where to find certain info such as bitrate, length in
seconds, etc, so when I am scanning my 100000 song library I don't have to
check bytes if the songs are obviously dissimilar. Thanks very much. Oh, and
I mostly do VB 6, though I do know some C++, so if you are going to talk
about file I/O stuff please refer to VB if you can. 

Silas
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