File's duration time longer than the recording time?

[raku]

Strangely, the files I have been exporting as mp3s, have longer duration times than the actual recordings.
For example, one recording, in the file info says it's an hour and a quarter but when I drop the file into itunes, it says its correct time of about 45 minutes.
Is there anything I can clarify here to figure out what's going on?
It's a mono recording and I have exported it as the default mp3 stereo or joint stereo (not sure about the difference).
Thanks for your help!

[kozikowski]

How long was the show when you performed it live?

Open the files in Quicktime and run the play slider most the way to the right and press play. Do you get the end of the show or something half-way along? What's the time listed?

We need a very serious opinion which ones are wrong.

Do they sound the same?

Koz

[kozikowski]

One more. Can you Export As WAV? What version do you get then?

Koz

[raku]

i'll have a chance to get to my computer to try these tonight.
thanks for your help.

[steve]

in the file info says it's an hour and a quarter but when I drop the file into itunes, it says its correct time of about 45 minutes.

And how long is it really?

Which version of Audacity are you using?

[raku]

hi steve,
I am using v. 1.3.3 beta for mac.
When I open the file in quicktime, it is of the correct length, about 45 minutes. Although the Preview duration says it is 01:14:44 in length (and the audio bit rate is 32000 as a compressed mp3!?).
Interestingly, when I export the file as a WAV, the duration in Preview is about the correct time and the bit rate is 705600.
Any ideas?
Thanks!

[kozikowski]

You may be fighting the Audacity default bit depth of 32-bit floating. That causes problems here and there.

Change in Audacity Preferences. The most trouble-free settings are 44100, 16-bit, Stereo. Restart Audacity for the settings to stick. All your exports from then on should be missing the "magic."

Koz

[steve]

the audio bit rate is 32000 as a compressed mp3

32kbps?

when I export the file as a WAV, the duration in Preview is about the correct time and the bit rate is 705600.

That's 44.1kHz 16 bit mono.

I suspect that the MP3 has been encoded with VBR (variable bit rate). VBR uses more "bits per second" on complex sounds, and less bits per second on more simple sounds. This allows better overall sound quality at a given bit rate than "Constant Bit Rate" (CBR) encoding. The down side is that some programs have difficulty working out the correct length of the audio. It all depends on whether the program is reading the duration from the header information of the file (which should be correct) or is trying to calculate the duration from the file size and bit rate (which will often be inaccurate).