Page 1 of 1

MP3 Export, CBR=Good VBR=Bad Length

Posted: Sat May 03, 2008 12:13 am
by gfaraghan
Possible bug in V1.3.4-beta

If I 'File-Export Multiple...-MP3-Options-Constant-256K' I get output MP3 files which are good; they play correctly and their metadata Length value is correct. By correct length I mean that Audacity editor timeline value = MP3 metadata value = MP3 player 100% progress bar value = MP3 player runtime value at end of song.
When I export VBR MP3 files the Length is Wrong and this causes playback and CD burning problems.

I first noticed this on an audiobook project when I tried to export 64K VBR Mono files. They were bad (I can't remember what clued me in, I was new to Audacity) but I then exported them 64K CBR and everything was fine. On my current project I again noticed VBR problems when outputing 256K, variable, stereo files and again redoing to CBR was fine. Here are my observations from first track of current project:
Audacity editor timeline value = 17:56
CBR MP3 metadata Length value = 17:56
CD burned from CBR MP3, CD track length = 17:56
VBR MP3 metadata Length value = 20:08

Using Windows Media Player 11.0.5721.5230:
MP3 player 100% progress bar value = 20:08
If you play song from beginning, song ends at runtime = 17:56, progress = ~90%
If you drag progress bar to ~95%, song ends at runtime = 20:08, progress = 100%
Burn to CD, play in boombox, track length = 20:08 BUT song finishes at 17:56 followed by SILENCE to 20:08

Using MediaMonkey 3.0.2.1134:
MP3 player 100% progress bar value = 17:56
If you play song from beginning, song ends at runtime = 17:56, progress = 100%
If you drag progress to ~95%, progress bar hits 100% at 17:56, song plays to runtime = 19:50
Burn to CD, burn process HUNG at end of track 1

Thus the erroneous VBR MP3 metadata Length value of 20:08 seems to confuse other programs/devices when they scale progress bars, allocate resources, write CD tracks, etc.

Hope this info is useful

Audacity V1.3.4-beta
Windows XP Pro SP2
Lame lame_enc.dll 3.97

Re: MP3 Export, CBR=Good VBR=Bad Length

Posted: Sat May 03, 2008 1:58 am
by steve
VBR = Variable bit rate. Many players display the time wrong for VBR files

For a CBR (Constant Bit Rate) file, it is easy for a player to work out exactly where it is in a song and hoow long the song is:
example

100 kbps CBR = 100,000 binary digits per second. After 1 second it will have played 100 kb, after 2 seconds, 200 kb, and so on.
100 kbps VBR = approximately 100,000 binary digits per second but varying depending on the complexity of the audio at any particular point in time. After 1 second it will have played 100 kb, or perhaps only 60 kb, or maybe 130 kb.
gfaraghan wrote:Thus the erroneous VBR MP3 metadata Length value of 20:08 seems to confuse other programs/devices when they scale progress bars, allocate resources, write CD tracks,
You should use WAV files for burning CD's for better quality. Also use a program such as Nero Lite for burning your CD's - it's MUCH better than using WMP.

Re: MP3 Export, CBR=Good VBR=Bad Length

Posted: Thu Feb 19, 2009 5:42 am
by nanonyme
Do note thought that despite all the nice arguments and suggestions, it's a bug, not a feature. Winamp so far has been the only player on both Linux and Windows that has actually been capable of showing file lengths correctly in VBR files. It seems that it simply ignores the incorrect file length metadata and calculates file length itself somehow.

Re: MP3 Export, CBR=Good VBR=Bad Length

Posted: Thu Feb 19, 2009 6:07 am
by steve
nanonyme wrote:Winamp so far has been the only player on both Linux and Windows that ....
WinAmp is not available for Linux, unless you are running it in Wine?
Rhythmbox on Linux shows the correct length.

Re: MP3 Export, CBR=Good VBR=Bad Length

Posted: Tue Mar 24, 2009 1:56 pm
by HFT
Wrong, I am using Rhythmbox 0.11.6 on Ubuntu (8.10 Intrepid Ibex) and it does not show proper lengths.
If it does on your system, that's very good, I'd love to know why.
Anyway, this is not consistent from one system to the other...
(I've been following this issue for 3 years now)

Have a good day!

HFT

Re: MP3 Export, CBR=Good VBR=Bad Length

Posted: Wed Mar 25, 2009 2:18 am
by steve
HFT wrote:I am using Rhythmbox 0.11.6 on Ubuntu (8.10 Intrepid Ibex) and it does not show proper lengths.
If it does on your system, that's very good, I'd love to know why.
"Rhythmbox 0.11.6 on Ubuntu (8.10 Intrepid Ibex) " - same here, and yes, on all the MP3's I've tested, play length are reported perfectly. Sorry, I've no idea why it should be different on your machine.
HFT wrote:Have a good day!
Thank you, I will. You too.

Re: MP3 Export, CBR=Good VBR=Bad Length

Posted: Fri Mar 27, 2009 8:19 am
by Gale Andrews
gfaraghan wrote:Possible bug in V1.3.4-beta When I export VBR MP3 files the Length is Wrong...
Hope this info is useful
1.3.4 is long obsolete so the information, well-intentioned as it is, is not at all useful.

If you upgrade to the current Beta 1.3.7, all these VBR inconsistencies should be fixed. Please note you will need to obtain the latest version (Lame_v3.98.2_for_Audacity_on_Windows.exe)

from:
http://lame.buanzo.com.ar/

following the instructions given here:
http://www.audacityteam.org/manual/inde ... ns#winlame

That page is also accessible from the "Download" button in the "MP3 Export Library" section of Import / Export Preferences.

If you are not already doing so, you can subscribe to receive occasional e-mails from us when we release new versions of Audacity. To subscribe, go to the bottom of our home page:
http://audacityteam.org/#announce

enter your e-mail address and click "Add".


Gale