Re: AAC Constant Bit Rate coding (Neil Waterman )


Subject: Re: AAC Constant Bit Rate coding
From:    Neil Waterman  <neil.waterman@xxxxxxxx>
Date:    Tue, 15 Nov 2011 08:33:31 -0500
List-Archive:<http://lists.mcgill.ca/scripts/wa.exe?LIST=AUDITORY>

Even when AAC is listed as CBR, the bitrate will still change. I like to think of it as quasi-ABR in that you pick a 128kbps CBR bitrate but the bitrate in the file can change +-3-4kbps while the overall average bitrate will remain at about 128kbps. I have used the Nero CODEC > http://www.nero.com/eng/technologies-aac-codec.html I don't have time to look at the options for VBR versus CBR for Nero right now... In general, with any lossy encoder, VBR is always a better choice than CBR. AAC is no different here. Nero's AAC encoder performs much better in a VBR environment. The iTunes AAC encoder dosn't benefit too much from VBR implementations but that is because Apple restricted it. With iTunes AAC, you pick a minimum bitrate and the encoder can change the bitrate +10-15kbps throughout the song. The overall bitrate will still remain near the target you selected. Nero AAC works with different quality levels (like Lame mp3) while iTunes AAC works with a known bitrate. Either way, enabling VBR will only help with the quality of the file. What is the reason for wanting CBR (which is pseudo-CBR!). - Neil On Nov 15, 2011, at 8:07 AM, fabien gouyon wrote: > Dear list, > > Could somebody recommend a free software, or even better some > open-source code, for converting audio from WAV to AAC with *constant* > bit rate (and not variable bit rate). > > Any help would be much appreciated. > Best, > > -- > Fabien Gouyon, PhD > Senior Research Scientist, INESC Porto > Invited Assistant Professor, Engineering Faculty, University of Porto > http://www.inescporto.pt/~fgouyon > http://smc.inescporto.pt/ >


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