Re: [Plib-users] Toying with Ogg

[Cameron M. <li...@to...>]

* sjb...@ai... [2001.06.29 00:20]:
> Cameron Moore wrote:
> 
> > I'm playing around with Ogg Vorbis at the moment, and I'm stuck trying
> > to figure out how to use it with plib.  My first goal is to use
> > slSample( Uchar *buff, int leng ) to play the stream.
> 
> Isn't that going to be a rather large file though?

If by 'file' you mean the .ogg file, then why does it have to be large?
What are you getting at?

> > The problem for this newbie is that libvorbisfile converts the .ogg
> > stream into a char[] buffer (PCM) but plib wants a Uchar* buffer.  Is
> > there a trick to converting between these datatypes?
> 
> Well, it depends on how Ogg translates that into a voltage.
> 
> If it's signed char, then probably  +127 is the max positive, zero is
> zero and -128 is max negative...as you'd expect.
> 
> SL is using 255 is max positive, 128 is zero volts and 0 is max negative,
> so, looking at the bit patterns:
> 
>    volts    Ogg          SL
>     +max    01111111     11111111
>             00111111     10111111
>     zero    00000000     10000000
>             11000000     01000000
>     -max    10000000     00000000
> 
> ...so you just need to flip the topmost bit of each byte...
> 
>    slByte = oggByte ^ 0x80 ;
> 
> Tadaaa!

You rock.

> But I think you really need to find a way for Ogg's output to continuously
> churn out bytes and feed them into SL...that's *hard* to do...but 2.4 Megabytes
> per minute of music is a heck of a lot of memory to burn.

That's probably more work than I want to do, but we'll see.  8-)  And
about the mem usage, how is ogg harder on memory than wav or au?
IIRC, Q3A uses MP3s for some of it's intro music and doesn't seem to
have any problems with it.
-- 
Cameron Moore