when I use --aps or a different vbr mode for encoding mp3 files with LAME what is the interval the encoder is 'guessing' the bitrate? I mean does it also use bitrates like '100kbps' or '171kbps' for some portions or does it only use preset bitrates like 96kbps, 128kbps, 160kbps, 192kbps etc.? I'm just looking at some graphs EncSpot provides and it only shows the common bitrates...so I was wondering if that was accurate or if it just rounds it off to the closest common bitrate.

Thanks

Hi,
For --aps the limits are 128..320kbps.

With mp3, for each frame, only a predefined bitrate (=> frame size) can be used. There could have been a waste of space, but fortunately there's the bit reservoir to smooth this out.

For example, take a simplified case when LAME determines 176kbps as the adequate bitrate for the whole song. The output file will have 50% 160kbps and 50% 192kbps frame, and the bit reservoir will take bits from each 192kbps frame, to put them into 160kbps frames. Thus the result will be mostly identical to 176kbps quality.

cool, thanks!