Now that the Feb SDK XACT is out, I see it now supports ADPCM. However, we would really like the Windows XACT to support XMA format on PC (like it does on Xbox360). We need the better compression rates that XMA gives over ADPCM. Is there any chance of this happening, or is XMA something Xbox-specific that will never be available on Windows?
Here's a more detailed response from Chuck Walbourn, one of our engineers, on the directx audio USENET newsgroup:
The PC platform does not have the acceleration hardware present on the Xbox This difference is handled by the build process from the source PCM files --
360 for making XMA (a form of WMA) a practical solution for general sound
effect compression. XMA/WMA is a highly complex variable bit-rate
compression scheme that is non-trivial to decompress on the fly, while ADPCM
is simple enough to not have a major performance impact. XACT offers ADPCM
on Windows as a general compression solution, while it offers XMA as a
general compression solution on Xbox 360. XMA on the PC would not be a
viable solution, which is why it is not offered by XACT.
used within the XACT editor interface, allowing you to target both platforms
with the same content. Obviously XMA can achieve much higher compression
ratios than ADPCM, but given that modern PC platforms tend to have a GB+ RAM
plus 256 KB+ VRAM vs the Xbox 360's 512 KB RAM plus 10 MB VRAM, this is not
as big a challenge as you might first think.
Chuck Walbourn
SDE, Windows Gaming & Graphics
Obviously XMA can achieve much higher compression
ratios than ADPCM, but given that modern PC platforms tend to have a GB+ RAM
plus 256 KB+ VRAM vs the Xbox 360's 512 KB RAM plus 10 MB VRAM, this is not
as big a challenge as you might first think.
The main issue for us is not performance but size. We're doing a downloadable game (800-1GB) that is 75% audio content, much of which is very compressable (i.e. speech). For this situation we need better than 3.5:1 ADPCM compression, so this will probably be the main reason we dont use XACT. Even MP3 would be better than ADPCM.
XMA/WMA is a highly complex variable bit-rate compression scheme
It's much more complex than mp3/ogg format?
that is non-trivial to decompress on the fly
mp3/ogg files plays perfectly on the today PC's, decompressing their data in the real-time in the many and many titles. We need a higly compressible sound format available in XACT for music storing and playback.
