Re: Ogg (Tremor) on low-end devices

Hi all,

Sorry for not having replied to this sooner, but it appears that
emails aren't making it to me from this list :(

To summarise what I think the state of play with Tremor/Tremolo is:

 * Tremolo is an (my) ARM optimised version of v1.0 of Tremor. It
runs faster than Tremor - my timings for how much are probably a tad
bogus due to the hardware I was testing it on, but I believe it to be
significantly faster.

 * Tremor has been upgraded a couple of times with bug fixes (it's
now at 1.0.2), and I've pulled those fixes back into Tremolo.

 * Tremor has also been upgraded with a low memory mode and a low
accuracy mode. The low memory mode, I haven't looked at in detail.
The low accuracy mode (which saves 50K of lib size due to reduced
tables) reduces the quality we get out. Supposedly it saves 15% of
CPU.

 * Tremolo has not been updated with the low accuracy mode, and I'm
in two minds as to whether it's really a good idea - one of the aims
of Ogg Vorbis is superior audio quality - do we really want to throw
that away in exchange for faster decoding? Anyway, my belief is that
Tremolo is still faster, as the tremolo ARM coding should be worth
noticably more than 15%.

 * The thesis referred to in the links posted by Fingolfin earlier is
interesting, but it's main claim appears to be "We used FFT instead
of MDCT and it went 8 times faster". It's a slightly suspect claim as
they apparently used an assembly FFT on a DSP and compared the time
to using the existing MDCT code on the same DSP, where the existing
MDCT is written to make use of a 32*32 -> 64 operation that that DSP
didn't provide.

Robin
-- 
Robin Watts,             Email: <mailto:Robin.Watts@xxxxxxxxx>
Warm Silence Software,   WWW:   <http://www.wss.co.uk/>
P.O.Box 28, Woodstock,   Tel:   01608 737172 (or Mobile: 07885 487642)
Oxfordshire, OX20 1XX    Fax:   01608 737172

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