[vorbis-dev] vorbis.com

[Segher Boessenkool]

Michael Smith wrote:
> 
> At 05:03 AM 12/30/00 +0100, you wrote:
> >Form the vorbis.com homepage:
> >
> >"Ogg Vorbis does not compromise quality for freedom. Its stunning
> >quality is coupled with aggressive features like fast bitrate scaling,
> >surround channels, and fast sample-granularity seek and decode."
> >
> >This makes me wonder...
> >
> >-- What is "fast bitrate scaling"?
> 
> Encoding at some bitrate (usually high), then scaling that down to lower
> bitrates (for streaming, etc.) at high speed. Without a decode/encode cycle.
> 
> The code isn't complete, but the format is designed to make it possible.
> Basically, each vorbis packet gets truncated (the packets have to be built
> specially to make this possible, but the code doesn't do that quite yet.)
> 
> I don't know the details of how this is meant to work, though, except that
> it's mostly codebook trickeruy.

I believe the method is: just truncating the packets, and losing the
high-frequency part of the music.

"Fast bitrate scaling" is not something I've heard anyehere else, so
I tought I'd like an explanation .

> >-- I've never seen anything in the source supporting surround channels.
> 
> The format supports multiple channels (and the code allows you to use this
> capability). It's up to the application using the codec to actually feed
> this data to appropriate speakers. So yes - vorbis does support surround
> sound, though only at a low level - the application level stuff isn't there
> yet.
> 
> Further features specifically for surround sound may exist in the future,
> too (channel coupling for multiple channels, etc).

Yet the website doesn't mention _these_ facts.

> >-- I don't think Vorbis can do sample-gran seeks (yeah, sure, we can
> >   emulate it, but anyone can, and it's not implemented at this time).
> 
> Since it's a transform codec, obviously the 'real' seeking is to the
> nearest block (packet). Emulating it is possible (as it presumably is with
> other transform codecs, though I don't know if anyone actually does it),
> and the code does this. See ov_pcm_seek(). There's also a faster function
> that just does 'rough' seeking.
> 
> Unlike some codecs (mp3 comes to mind...), vorbis is capable of producing
> (as output) the same length (in samples) of data as the input - hence "fast
> sample-granularity [...] decode".

But that's something different from what you're saying.

The reason I'm compaining is simple:

-- Vorbis is open

o

-- Vorbis' advertisements should be open

...in the sense that they should be 'true', not marketing-directed.

Some time ago, someone at (I think it was) slashdot said, the true
challenge of open source is, it should be better than it's competitors
in _all_ respects. I think marketing is one of them :-)

I don't think Vorbis will be a bigger success because of making
misleading statements.

Cheers,

Segher

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