mp3 duration wrong ?

[dualboot]

Hi All,
I'm using version 1.3.4-beta(unicode) on Ubuntu 7.10 (64 bit).
I've started moving my LPs to MP3. When I export the tracks to MP3 with "export multiple", their length looks OK in the properties/audio tab of Nautilus (Ubuntu 7.10), but in Rhythmbox the length shows a shorter value. When the progress bar gets to the end, the audio continues playing until the real end of the track (not a big problem). ITunes on windows exhibits the same behavior. The real issue is when I move the track to my Ipod. This will skip on to the next track when it thinks the track has finished.

One reason I thought why it might have happened - trying to be clever, and save time I recorded my albums at 45rpm and then used audacity's effect/change speed to slow it back down. I've just tested without using the 'change speed' and the duration field in Nautilus is still different to that shown in rhythmbox (and in fact different to the 'selection length' shown at the bottom of the Audacity window as well ! )

Can anyone shed any light on this - there seem to be two different 'length' fields - how does Audacity set them ?

[steve]

Try Exporting as "CBR" MP3 (Constant Bit Rate), rather than the default "Variable" Bit Rate, and see if that solves the problem.

[dualboot]

Yes - thats sorted it. All values now match. Should I raise a formal bug ?

Is there any easy way to correct the stack of albums I've already done ?

[steve]

It's not actually a bug, at least not in Audacity.
MP3 encoding is done outside of Audacity with LAME, but I don't think the problem is with LAME either. The problem is that applications and mp3 gadgets will try to estimate the length of a track from the file itself, but they often have trouble with VBR.

With CBR it is easy for them to calculate the length by simply dividing the file size by the bit rate, however it's not so simple with VBR because the bit rate Varies.