>
> I normaly use -h -k -b 192 -ms for encoding. If I change -b 192 to
> --abr 192 i get files with average about 180-182kbit (about 45% frames
> at 160 and 10% above 192). Is the reason for this bits that was wasted
> in CBR before ?
>
Here's a simplified explination of what happens in CBR:
most frames are encoded at 90% of full bitrate (about 172kbs in this
example), with the extra 10% added to the reservoir. If the reservoir
becomes full, then LAME will start using 100% of the bits available.
The occasional hard-to-encode frame will use 100% and bits from the
reservoir.
So for CBR, the actual bits used for each frame depend on how
heavily the reservoir is used. If the reservoir is often being
used and built back up, there will be lots of frames using bits
equivelent of 172kbs. But if the reservoir is never used, most frames
will be using the full 192kbs, and only a small percentage will be at 172kbs.
ABR will encode all the "easy" frames at 172kbs, (using the reservoir
and a combination of 160 and 192kbs frames), and use larger bit
rates for the hard-to-encode frames.
So both ABR 192 and CBR 192 have the same worst case scenario: many
frames encoded at around 172kbs. ABR wins in the best case scenario
since it will always have extra bits avialable even if the reservoir
is empty.
> If its not, which parameters should be used if you want files that
> only go below 192 if its caused by bits otherwise wasted in CBR ? (To
> ensure that you with ABR *always* get a better result than with CBR)
>
So I would stick with ABR 192kbs if you are happy with CBR 192kbs.
But to guarantee every single frame of an ABR encoding is at
least as good as CBR, you would need to use "--abr 211"
(192 + 10%)
One last thing: ABR is very new. No bugs have shown up so
far, but it hasn't been thoroughly tested.
Mark
--
MP3 ENCODER mailing list ( http://geek.rcc.se/mp3encoder/ )
