---------------------------------------------------------------------CBR mode is gone from ogg encoder.
---------------------------------------------------------------------
I don't think so.
Ah, yes -it never really had it.
What it did have was "managed bitrate options" and a "-b" switch to aim the encoding toward an
average bitrate. -This is what you are thinking of. It appears to be the same thing as CBR but it is not.
fyi: The managed bitrate options allow the setting of a maximmum or minimum bitrate. The encoding algorithm doesn't actually have a "CBR mode" but by using these you force the encoding towards a certain target bitrate. These modes are still available (and I don't think they will change this) through the "-m and -M" command line switches.
However use of the managed bitrate engine is not recommended as it bypasses the whole point of Vorbis quality tuning.
---------------------------------------------------------------------
Why would you WANT CBR??? It sucks!
---------------------------------------------------------------------
VBR (or more exactely "quality mode") is the default mode now.
CBR is useful for streaming since VBR mode can jump up to very high bitrate without any control.
Again the whole Vorbis encoding engine is built around the concept of VBR. The introduction of the "quality mode switches" in RC3 (Dec 2001) was a move to try and get people to forget their fixation with bitrates and the notions of "this bitrate equals that quality-of-sound" -the most typical being the commonly held belief that 128kbps mp3 equal CD quality! (I hope no-one here still perscribes to this rubbish).
So the tuned part of the RC3 engine was linked to the "-q" (or "quality mode" as Michel mentioned) option, where previously the "-b" (for bitrate
) was used to explicitly select the target
average bitrate (or "nominal" bitrate) the encoder should aim for when encoding.
Yes, even though this opion was -b like that of many mp3 encoders' CBR mode, it was actually producing "VBR" files that had an
average bitrate NEAR the given figure.
O.K, after thinking about it there are (very few) cases where the
managed bitrate modes would be useful:
Streaming:
-I agree that bitrates can (and should) jump up in a VBR encoder, however it is exagerating a little to say they do this without any control. -The control is in the quality level setting. This gives a file with an average bitrate "tuned" to that level of quality appropriate for that particular file. -Again the managed bitrate engine also allows more control by setting a maximum bitrate.
-I can see no reason why VBR wouldn't be suitable for streaming, other than requiring filesize to be small. For this the -M (maximmum bitrate option) would be fine. The encoder then would not waste bits on easy to encode parts (like silence) but would not use more than -M
on the hardest to encode parts.
Fixed-size channels:
-O.K. this is about the only place I can think of that warrants the existance of the -m (minimum bitrate) mode. The -m and -M and -b switches can be used together to restrict the encoding toward a particular bitrate, -but this is really forcing the engine to do something it was (rightly) not made to do. I personally don't like the idea of minimum and maximum bitrates as they mean either bits are wasted where they shouldn't be, or are not being used where they are needed -or both!
For example, I know a lot of people are using -q4.99
Because at q5 oggenc stop to do "join channel stereo".
Yes, this is true that at -q5 Vorbis kicks in LOSSLESS Channel coupling! Very cool. (however it means a filesize jump from q4.99-q5.00)
Also at -q6 there is NO lowpass filter, so there is asize jump again at q5.99-q6.00.
(although there is not really much of a lowpass filter above q4 anyway)
happy ogging! 
peleton.
Author
Topic: OGG is gold ! How about a new encoder plugin ? (Read 1617 times)