[freebsd-questions] Scanning MP3 files for skips

Chuck Swiger cswiger at mac.com
Tue Jun 13 15:09:30 UTC 2006

Howard Jones wrote:
> Chuck Swiger wrote:
[ ...ID'ing skips in music... ]
>> Sort of...GraceNote and a few other companies ("Shazam", seems to be
>> from India?) sell a service where music files can be fingerprinted and
>> identified.  Good audio files ought to ID as what they are; bad music
>> files with skips or garbage will fail to ID.
> Shazam (at least) works on a fragment the song. In the UK they provide a
> phone-based service, which only needs 20-30 seconds of clear music to
> identify a song.

Yeah, that's right.  But there's also a fingerprinting tool which creates 
something called QCF files (Qualcom something-or-other) which analyses the 
entire song and should notice major skips or distortions better.

[ ... ]
> I'm also looking for a blip-detecting MP3 tool. I haven't had time to
> look at it yet, but I was going to try something like libmad on the
> assumption that somewhere internally it knows when it's only had half an
> frame of data, even if there is no CRC. That way, it'll work on any
> obscure music I have, without relying on some external giant database of
> correctness.

That's the rub of the matter: most home-grown tools are going to find it hard 
to recognize a skip from Trent Reznor or a lot of rap music, or a dropout with 
silences common in classic music, etc.  :-)

With the external giant database of correctness, you've got something which 
actually can tell that a song isn't correct, rather than making guesses, even 
if you have to break your samples down into 10 to 30 second pieces and check 
them all individually.

[ Again, I would try using the QCF fingerprinting tool instead of exhaustive 
submatch checking.  On the other hand, if you can manage to put together 
something which can guess well, I'd be interested in seeing it... ]


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