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Discrepancies in MP3 file sizes

 
 
Reply Sat 30 May, 2009 04:01 pm
I have the same song twice as an mp3

I'm trying to figure out the discrepancy in their sizes
File 1
len 4:00
size: 9406kb
bitrate: 320
sampled 44khz stereo

File 2
len 4:02
size: 6247kb
bitrate: 320
sampled 44khz stereo

I thought that file size (in kb) = len (in seconds) * bit rate/8,000
ie 8 bits to a byte and approx 1000 bytes to a kb

And that would make file 1 about right.

Both play to completion.

Why the huge discrepancy - is the second file VBR (variable bit rate)? I can't see that flagged anywhere in the file properties - how could I tell?

Are VBR files the same quality?
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View best answer, chosen by hingehead
Robert Gentel
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  2  
Reply Sat 30 May, 2009 06:01 pm
@hingehead,
hingehead wrote:
I thought that file size (in kb) = len (in seconds) * bit rate/8,000


That would be a "constant bit rate" which differs from "average bit rate" and/or VBR (as you have guessed is the cause).

Quote:
Why the huge discrepancy - is the second file VBR (variable bit rate)? I can't see that flagged anywhere in the file properties - how could I tell?


There can also be meta data embedded in the file (e.g. ID3 tags) but these typically have low limits on how much data can be stored this way (though some could easily account for this discrepancy, as their tags can be hundreds of megabytes).

As to how you can tell, I know of one way off the top of my head, which is to play it in win amp, some versions of which I remember displaying bitrate throughout the song.

BTW, if you are doing high bit rates like that, I recommend moving to a lossless codec. At those bitrates you are pretty much what a lossless codec would give you in terms of file size.
hingehead
 
  1  
Reply Sat 30 May, 2009 07:28 pm
@Robert Gentel,
Thanks Robert will check if I can see bit rate displaying while playing in WMP

Which lossless codec is the most 'frugal' with disk space?

I've got some flac files but the sizes are considerably higher. I also miss the metadata options (well at least the ones WMP can use).
NickFun
 
  2  
Reply Sat 30 May, 2009 08:23 pm
I find that among the larger files there are usually porn videos embedded in which you need a special program to access. But I'm sure it's worth it!
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Robert Gentel
 
  1  
Reply Sun 31 May, 2009 03:38 am
@hingehead,
hingehead wrote:
Which lossless codec is the most 'frugal' with disk space?


Here's a comparison, the differences are slight:

http://wiki.hydrogenaudio.org/index.php?title=Lossless_comparison#Comparison_Table

Quote:
I've got some flac files but the sizes are considerably higher. I also miss the metadata options (well at least the ones WMP can use).


Yeah, I may have overstated that a bit, flac should still be significantly higher, especially if the mp3 is using variable bit rate. What I meant was that if you can really tell the difference between 160 and 320 then I'd think you would want the lossless quality.

I personally am not an audiophile, and can't tell the difference beyond 160 unless there are artifacts, but you may want to try Vorbis for a better lossy codec than mp3. Personally, I use mp3 exclusively because it's the only one that has played in every program and player I've ever seen but if quality is a huge factor for you there's probably better codecs for you than mp3 even in the lossy world.
hingehead
 
  1  
Reply Sun 31 May, 2009 08:36 pm
@Robert Gentel,
Hi Robert

Thanks for the comparison link - I never realised WMA was lossless (I'm guessing it isn't unless specifically told to be - because i have 128kbs wma files that sound like 160 mp3s.

I'm with you re mp3s - maybe not gold but definitely standard. I can definitely hear the diff between a 320 and a 160 (even 192/224) - but I'm not an audiofile.

I was about to ask a question, but it probably deserves it's own topic - so hopefully I'll see you there.

Thanks again.

PS I never did find that realtime bit rate display in WMP.
Robert Gentel
 
  2  
Reply Sun 31 May, 2009 09:35 pm
@hingehead,
hingehead wrote:
PS I never did find that realtime bit rate display in WMP.


It wasn't WMP but rather WinAmp.
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