Re: [Plib-users] Toying with Ogg

[Steve B. <sjb...@ai...>]

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?

> 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!

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.

----------------------------- Steve Baker -------------------------------
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