Subject: Re: [linux-audio-dev] decoding mp3 files
From: Paul Davis (pbd_AT_op.net)
Date: Fri Jun 07 2002 - 19:24:44 EEST
>Hello.
>
>I have encoded a wav to a mp3. But when decoding it back, the wav is slightly
>bigger as the original.
>
>for example:
>$ ls -l
>-rw-r--r-- 1 kristian adlib 4079698 Jun 7 14:24 H-diff.mp3
>-rw-r--r-- 1 kristian adlib 44969704 Jun 7 15:03 H-diff.wav
>-rw-r--r-- 1 kristian adlib 44965580 Jun 5 13:58 H-src.wav
>
>I read in the lame-FAQ that this is the intended behaviour. (Cause of some tec
>hnical reason I don't understand yet.) Are there some differences between all
>the decoders out there ?
>
>I'm currently writing a program that compares wav's and saves the differences
>to another file. So it's reasonable bad having an extra chunk of bytes at the
>beginning of the data in the wav-file. Is there any specification how to ignor
>e these extra bytes or to know the size of this extra chunk ? (It's no problem
> ignoring extra bytes at the end of the wave...)
i don't know precisely whats going on there, but mp3 is a *lossy*
compression technique. whether or not the data size is the same or
not, you will not get the same data back after the mp3 cycle as you
started with. this isn't a decoder-specific issue - its inherent to
the way mp3 works. comparing two wavs that have been through this
process will never find them to be the same.
--p
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