When making mp3's extra length is added

[Swartling]

I just noticed that extra length is added (0.160) to the total length, when creating mp3 files from both aif and wav.

why is that?

Normally I use quick time converstion in Pro Tools both for export files and bounce, and with the same result: extra length is added. And same thing when converting aif/wav to mp3 in iTunes, and same in Logic. I also run into the same problem in another studio. Asked our local support and they couldnt tell either...they had the same result.

Right now I'm not in my studio, so I can't say all my versions of software. I use mac, pro tools, mojo...

But some one might have run into the same thing.

Have Apple done anything with the Quick time codecs??

The problem is that when we deliver radio commercials in Sweden we do that in mp3 formats, and a 30s spot can not be 30.160 s., it should be 30.000s

All best!

John

ps) couldn't find anything in the forum about this, so please sorry if this has already been discussed.

[Eric Seaberg]

We use BarbaBatch for all of our encoding and I discovered this when version 8 was released with the better graphic resolution of the waveform. I believe there's additional data within the file that is doing this.

The way we got around it is to export the file within PT and encode that instead of encode the file that's in the session.

I assume you're working with 16-bit sessions, too, as you wouldn't want to MP3 24-bit files.

[KMcK]

If they must have MP3 (why would they want compressed format?) at exactly 30 sec, then make your files .160sec shorter before you convert (or whatever length you figure out equals 30 sec after conversion). The extra time is inherent within the MP3 format, and there is nothing you can do that will prevent that from happening. Every MP3 encoder will add that extra time, doesn't matter which one you use, as long as you use the MP3 format you will have extra silence at the beginning and end of the file.

There are actually a few threads buried in the DUC about this, but most are pretty old and now have broken links. This is the best thing I could find of it being discussed in more detail:

http://audacity.238276.n2.nabble.com...-td289876.html

[Rich Breen]

Originally Posted by Eric Seaberg

We use BarbaBatch for all of our encoding and I discovered this when version 8 was released with the better graphic resolution of the waveform. I believe there's additional data within the file that is doing this.

The way we got around it is to export the file within PT and encode that instead of encode the file that's in the session.

I assume you're working with 16-bit sessions, too, as you wouldn't want to MP3 24-bit files.

MP3s (and AACs) are not reliable WRT timing, and are not suitable for professional applications for this reason amongst others - audio can start anywhere within an encode frame, and different encoders pad start and end differently. If you want exact timing you should be using .wav or .aif.

best,
rich

[tj_davies]

Originally Posted by Swartling

I just noticed that extra length is added (0.160) to the total length, when creating mp3 files from both aif and wav.

why is that?

Normally I use quick time converstion in Pro Tools both for export files and bounce, and with the same result: extra length is added. And same thing when converting aif/wav to mp3 in iTunes, and same in Logic. I also run into the same problem in another studio. Asked our local support and they couldnt tell either...they had the same result.

Right now I'm not in my studio, so I can't say all my versions of software. I use mac, pro tools, mojo...

But some one might have run into the same thing.

Have Apple done anything with the Quick time codecs??

The problem is that when we deliver radio commercials in Sweden we do that in mp3 formats, and a 30s spot can not be 30.160 s., it should be 30.000s

All best!

John

ps) couldn't find anything in the forum about this, so please sorry if this has already been discussed.

Hi John,

30.16s is the length when importing back to Pro Tools. Quicktime Player says 30.06s. I think Pro Tools imports all data stored inside the mp3 (as silence) whereas QT subtracts the data and only shows the added silence due to rounding as an additional time (so 100ms of data, 60ms of rounding). This is a known issue:

This has to do with rounding and id tags of mp3. Here in Germany, radio stations also require mp3, and have never alerted an error, because the mp3 is a bit longer than required. I bet they know about this issue themselves.

By the way, the delay differs from material to material, so you can't just playout 160ms shorter signals.
And if you want gapless mp3 for looping - forget it. This is a known problem and there are scripts for Flash to jump to the correct position to play the loop correctly - therefore always deliver wav or aif for loops created in Flash.

Apple noticed this problem in the beginning of iTunes themselves - e.g. when playing Live CDs the gap between tracks (ongoing applause) was noticeable due to a short bit of silence. Apple updated iTunes and included a workaround, that would jump past the additional gaps in mp3s.

Have you tried delivering the mp3 to the radio station? I would assume they won't let them bounce back.

Hope this helps a bit,
Timothy