mp3 bounce adds to file length?

[bogasproductions]

I notice when bouncing to mp3, there is a small increase in file length (around 0.3 seconds, not consistent). This became obvious when I attempted to bounce out audio which is trimmed for looping, and discovered this extra silence on the end of the file. Bouncing out in other formats (WAV, AIFF, etc.) I don't encounter this problem. This doesn't appear to be a ProTools glitch, but more a function of some weird mp3 issue. Anyone?

[Eric Seaberg]

I've noticed that as well, and we use BarbaBatch for all of our encoding. I suggest it is from the extra data in the file for PT8's new HiRez waveforms!!

I have confirmed this theory by renaming a Record-to-Session mix slightly before the RIGHT channel file has completed its redraw, according to the task manager. Then when I go to the PROJECT window, the Left and Right files are now different sizes with the Left (completed the redraw) being larger.

Funny thing is, with a LONGER file, i.e. a typical 26:00 minute radio show like what we produce, the MP3s show a total length of almost 28:00 minutes although they only PLAY for 26:00.

By the way, this 'length extension' does happen to ALL FILE TYPES, WAV and AIFF included. Stop the redraw of one of the channels as I did above and you'll see the difference.

Digi, can you confirm this concept?

[Mark Ziebarth]

I would have guessed the fixed frame size of MP3 files is the reason for the length extension, but maybe the concept Eric described is true...
(I'm still on 7.4 and never experienced problems with WAV or AIF looping)
I often encountered problems with looping and MP3. Other codecs like AAC and Ogg Vorbis don't alter your file length.

Kind regards

Mark

[Eric Seaberg]

You won't find the problem prior to PT8. That's when they added the HiRes waveforms that are re-drawn EVEN after recording. It's really a time waster in many cases.

[Frank Kruse]

Originally Posted by bogasproductions

I notice when bouncing to mp3, there is a small increase in file length (around 0.3 seconds, not consistent). This became obvious when I attempted to bounce out audio which is trimmed for looping, and discovered this extra silence on the end of the file. Bouncing out in other formats (WAV, AIFF, etc.) I don't encounter this problem. This doesn't appear to be a ProTools glitch, but more a function of some weird mp3 issue. Anyone?

Itunes does this too. Never trust iTunes MP3 conversion when lip-sync in crutial and the recipient is going to spot the file to a certain TC-position.

[Eric Seaberg]

ANYTHING will do it, as I said, if the original file comes from ProTools 8.

[mgrimm]

Originally Posted by Eric Seaberg

You won't find the problem prior to PT8. That's when they added the HiRes waveforms that are re-drawn EVEN after recording. It's really a time waster in many cases.

Actually this isn't entirely true. Although I'm unsure about the HiRes waveforms (thought they kept all that info in the wavecache) try encoding an mp3 with any other program (Barbabatch, Soundforge, iTunes) and you'll find it does the same thing.

Mark Ziebarth is correct:

"I would have guessed the fixed frame size of MP3 files is the reason for the length extension, but maybe the concept Eric described is true...
(I'm still on 7.4 and never experienced problems with WAV or AIF looping)
I often encountered problems with looping and MP3. Other codecs like AAC and Ogg Vorbis don't alter your file length."

Mp3 compression requires bits of header data before and after all audio data, which makes looping mp3's very difficult.

In game development, many middleware audio solutions have algorithms to compensate for this (e.g. Wwise and Fmod.)

[bogasproductions]

Thanks for all of these responses. This problem does not appear when bouncing in any other format, i.e. WAV, AIFF, etc., so the fixed frame size looks like the answer. Looks like I may have to finally buy BarbaBatch...

[DigiTechSupt]

Hey guys - I know you've been around long enough to understand that Google is your friend. All MP3 encoders add 'padding' to the beginning and end of songs. Here's a good explanation from the LAME MP3 encoder FAQ:

http://lame.sourceforge.net/tech-FAQ.txt

[Eric Seaberg]

But I didn't see this problem until PT8 and we've been using BarbaBatch with LAME for years. If you try to play the MP3 in the Finder (select it and hit the space-bar) it will show you MUCH more play time than is actually there.