[vorbis-dev] Transient coding: AAC vs. Vorbis

[Segher Boessenkool]

>> You *can* have different transforms in Vorbis I files; they just
>> won't be "standard", and so can't be decoded by standard decoders.
>
> ...and is of no use for me and my hardware player ;)
> What's the point ? I do know that Vorbis I has a placeholder
> for identifying a transform. So what ? What's the use of
> a modified and incompatible Vorbis I stream ?

Improved audio quality by experimenting?  Hey, if everyone just
sits back and waits for Vorbis II, it'll never be there ;-)

>> And in 32kbps/channel you only have _NINETY-THREE_ bits per such
>> a block _total_.
>
> true. but
> in case of a 93 bit packet this one bit does not hurt since
> the whole packet has to be stored in octets ;)

Except that we're not fixed-size-per-block -- 94 bits per block
on average is exactly 1 bit per block bigger than 93 bits per
block average, even when padding every packet to a multiple of
8 bits.

> first, this "sort of blocking" is more a generalisation which
> enables us to use packets that store 128,256,384,...,1024
> samples per channel - not just 128 and 1024.

That's a very nice feature.

> So, the ability to store
> more short windows in one packet that share a floor curve
> and/or the codebook classification codes because of a locally
> static behaviour of the signal is an obvious improvement to
> me.
>
> second, the packets are still independently decodable.

Not if they share the floor curve etc.!

> I just wanted to share this idea because I think this is one
> of those things that needs to get improved for Vorbis II and
> to make sure, that this will be addressed somehow.

It sounds like some of these things might help.  But someone
will need to implement an experimental version of it and try
things out...


Segher