[Vorbis-dev] Performance on low-CPU devices

[Michael Smith]

On Wed, 12 Jan 2005 15:26:40 +0100, Martin Vilcans <martin at jadestone.se> wrote:
> Hi!
> 
> I'm new to this list. I work at a game development company, and we are
> considering Ogg Vorbis for the audio in a cell phone game. Does anyone
> here have any figures or educated guesses on how much CPU power the
> decoding requires? I guess Tremor is the decoder to use, as the CPU
> doesn't have a floating point unit, but will it be possible to use it
> for playing background music in a cell phone game?

Yeah, Tremor would be the one to use. You can certainly decode on
(modern) cell phones, but whether it's appropriate really depends on
how much cpu you can afford to use on the music. Tremor also has a
low-mem version, which is designed to work in extremely memory
constrained environments, but that uses a little more cpu - a cell
phone probably has enough memory that you're better off using the
faster version, but maybe that's something to experiment with.

There's a Tremor mailing list too - if you end up deciding to use it,
and you want help with getting it up and running, that's probably a
better place to ask.

> 
> The target platform has an ARM at around 100 MHz. Any ideas about how
> much of the CPU would be used for decoding? Is it faster to decode lower
> bitrates and/or lower sample frequencies?

For CD rate audio (stereo, 44.1kHz), you'll use a lot of that cpu.
Maybe up around 40-60% (I really don't know precisely). However, it's
likely that you don't really need cd-quality audio, and using fewer
channels (i.e. mono), and lower sample frequencies will dramatically
reduce the cpu load. Lower bitrates also help, but to a much smaller
degree.

It's really hard to say whether this is ok for your uses - it depends
on what sort of audio quality you're aiming for, and how much of your
CPU you're willing to use up on music, and of course on the precise
details of the device. You're best off experimenting, and then asking
more specific questions down the track.

Mike