A bug?? Non identical MP3 encoding of same track

[usenfixit]

I wanted to test if MP3 encoding directly from CD or from extracted wma lossless gives the same result.

answer no.

 

What I did.

1/ With Switch Sound File Converter v 2.01, convert a CD track to MP3 VBR128-320kb joint stereo highest quality(0) and name it 01 VBR128-320kb.mp3

2/ With Windows Media Player 11 extract the same CD track in WMA lossless mode, resulting file is 01 WMP11.wma

Then use Switch on that WMP11.wma to convert to MP3 with same parameters, result is 01 WMP11.mp3

3/ With JetAudio 7 extract the same CD track in WMA lossless mode, resulting file is 01 JetAudio.wma

Then use Switch on that 01 jetAudio.wma to convert to MP3 with same parameters, result is 01 JetAudio.mp3

4/ With MP3TagTools, remove all ID tags(v1&2)

5/ With Media Tagger, remove all wma tags.

6/ Compute hashing values (SHA256)

 

Well that's the result

01 JetAudio.wma & 01 WMP11.wma have the same hashing result - OK, so JetAudio & WMP providing same encoding

01 JetAudio.mp3 & 01 WMP11.mp3 have the same hashing result - OK, normal has sources are now proved to be identical

01 JetAudio.mp3 & 01 VBR128-320kb.mp3 do NOT have same hashing value ....

So as if encoding directly from the CD or from the lossless extraction was not the same.

 

Actually the 01 WMP11.mp3 is 4 274 999 bytes, whilst the 01 VBR128-320kb.mp3 is 4 274 895 bytes

 

Why??