[vorbis] Is Vorbis really THIS good?

[Gian-Carlo Pascutto]

----- Original Message -----
From: "Jernej Simonèiè" <jernej.simoncic at guest.arnes.si>
To: "safemode" <vorbis at xiph.org>
Sent: Thursday, October 11, 2001 11:34 PM
Subject: Re[2]: [vorbis] Is Vorbis really THIS good?

11. oktober 2001, 23:08:13, you wrote:

> Would be nice to see oggenc or some other ogg encoder with the abiltiy to
s> encode at whatever bitrate is necessary for the ogg to sound good.
Instead
s> of guess and checking that is necessary now (which slows down encoding
ogg
s> files for cds quite a lot unless you dont care about space/quality
s> tradeoffs).  There is no one bitrate fits all.  Lame accomplishes this
with
s> mp3.

>You mean something like real, quality based VBR, and not current
>kindof-ABR?

The current encoding modes are really VBR, but the way things work
internally hides this from the user mostly.

For example, when playing Oggs with Winamp it seems as there are
only very small fluctuations in bitrate. If you try ogg123 you will
see that they are actually much bigger.

Another thing is that it looks as if you encode by bitrate, but
that isn't actually true. Internally the current libs don't care
about bitrate at all, and use preset encoding modes based on quality
levels.

Because Vorbis bit allocation is much more advanced than MP3, and
the preset modes in RC2 are so stable, those quality levels usually
turn out to average around a certain bitrate, which is why they appear
ABR, but they really aren't.

When you compare to MP3, keep in mind that, for example, to encode
frequencies above 16kHz, MP3 encoding gets very varying bitrate
requirements (has to do with a limitation in the format, you can
read about it on the LAME mailinglist or r3mix.net forums), which
causes the wide bitrate fluctuations you see. Vorbis has no such
limitation, and can do with a lot smaller fluctuations.

My mode (and possibly some of the modes in RC3, from what I've heard)
is a bit more aggressive in certain circumstances, which cause
wider fluctuations, and hence appears more VBR-like.

RC3 will also feature a bitrate management engine, which makes
CBR encoding possible, and probably other interesting CBR/ABR/VBR
tunings.


--
GCP

--- >8 ----
List archives:  http://www.xiph.org/archives/
Ogg project homepage: http://www.xiph.org/ogg/
To unsubscribe from this list, send a message to 'vorbis-request at xiph.org'
containing only the word 'unsubscribe' in the body.  No subject is needed.
Unsubscribe messages sent to the list will be ignored/filtered.