[Vorbis] Simple Codec questions

[xiphmont at xiph.org]

> - What is the expected highest compression ratio where no noticeable
> degradation occurs yet?

Highly listener dependant.  And the best compressions are not fixed-ratio.

> I need something like 1/8th compared with wave data.

That is realistic for Vorbis, in fact, it's much lower compression
than most people would consider transparent.

> - Is it possible to access the decoded streams for further processing
> outside of the codec? If yes, can the data be decoded to wave format?

Compressed format -> WAV is what a decoder is.  Some minor
manipulations are possible without a full decode/reencode cycle, but
not many.  Compressed formats like mp3, Vorbis, AAC, etc are 'last
mile delivery' formats.  They're intended to be the final package that
is never further manipualted, and certainly not
decompressed/recompressed.

> - Can the codec run on an embedded hardware using ARM processor?

Yes.  Vorbis decode was first ported to ARM in 2001.

> What are
> the hardware requirements? The minimum memory usage? The processor load?

The vorbis encoder has not been widely ported.  The decoder port
depends on the ARM implementation in use.  There are two basic types
as far as Vorbis is concerned; ARMs that use offboard DRAM and those
that are restricted to using only on-core SRAM.  The two ARM ports of
Vorbis decode (the Tremor decoder) trade memory use/CPU.  The
large-memory version requires about 200kB working memory and ~ 50MHZ
of an ARM7.  The low memory version uses ~ 40kB of code and 45kB of
working memory and needs about double the CPU of the large memort
version.

You may also want to look into our new Opus codec that reaches Vorbis
quality levels for most samples and has lower CPU and memory
requirements.

Monty