[Openal] ADPCM

[William Stewart]

Garin

You raise an issue I thought would also be interesting for me to  
comment on.

With Tiger, Apple has also described a new audio file format - CAF  
(Core Audio Format) Files.

There are a few fundamental issues we wanted to tackle with CAF:
(1) Should be audio format agnostic
     - store anything from LPCM (big or little endian), 1-bit audio,  
AAC, MP3, Ogg, Lossless (Apple, FLAC,..), etc...
(2) 64 bit clean data sizes
(3) Efficient and extensible
(4) Rich meta-data

It could fit in well with both the content and platforms that OpenAL  
supports, so might have some value here as well.

There's a spec document available at Apple's developer web site:  
http//developer.apple.com/audio (just do a search for CAF Files)

We anticipate making this broadly available (including sample code to  
read these files that is platform neutral). In the meantime, Mac OS X  
Tiger ships with support for reading and writing these files with the  
AudioFile API. QuickTime 7 also offers support for reading these  
files on previous Mac OS X (Panther) and Windows.

Thanks

Bill

On 24/06/2005, at 4:12 PM, Garin Hiebert wrote:

> Great points from Bill.  I'll add a few more comments that come to  
> mind...
>
> While stunningly efficient, ADPCM quality is pretty bad.  Just  
> worth taking into account.
>
> My limited experience with Ogg Vorbis seems to confirm points from  
> Bill's post -- slightly better quality than MP3 for the same  
> compression level, and pretty much the same in CPU hit (although  
> Ryan's custom AL implementation for OS X should be even _better_  
> because his implementation skips unneeded float-to-int-to-float  
> conversions).
>
> One thing that I think is really good about Ogg Vorbis is that  
> their "vorbisfile" API is really simple (yet flexible).  We've used  
> it for several projects here at Creative, and really found it to be  
> very easy.  How good things are on the API front with AAC I don't  
> know, but with the lower CPU hit it is probably worth finding out...
>
> Garin
>
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