AW: [vorbis-dev] PlusV algorithm -> CBR

[Carsten Haese]

On Wed, 2003-01-29 at 09:52, Hannes wrote:
> If you consider a streaming application an exotic environment, OK.
> Personally, I don't.
> 
> I don't know if you actually know what vorbis is capable of in respect of
> realtime internet streaming, but you are really *only* missing a correct CBR
> to put you in front of the race. Vorbis is a really great codec - I value it
> over most of the available codecs at the moment - but it is a shame that you
> simply cannot rely on some modes when you are intending to send your stream
> over e.g. a modem line.
> 
> I know it would mean a great deal of damage to vorbis quality, but would it
> really be so bad considering the possibilities? And if, how big would the
> bandwidth adaptation window really have to be - 2 seconds? thats about 1.9
> seconds too long, if this adds on my streaming latency, sorry.
> 
> I mean not to upset you because I know it doesn't work like this if you want
> vorbis quality - but isn't there some kind of compromise? The reason I'm
> writing you is that we are using vorbis as one of our codecs for an internet
> radio demonstrator. We would like to use the 45kbit/s-mode for HiFi-Stereo
> over ISDN (with all 20%FEC and Headers it normally sums up to 60-62 kbit/s).
> Sadly the 45kbit/s-mode sometimes behaves like a 64kbit/s vorbis, meaning
> that for a lot of slow, montone passages it really keeps its speed limit,
> but if the going gets rough, bandwidth goes up. This made us decide to use
> the 32kbit/s-mono-setting, which is kind of sad, really.

Correct me if I'm wrong, but strict CBR should not be necessary for
streaming. Vorbis does allow you to specify a maximum bitrate, and from
your description it is not clear whether you have done that.

If you are using the maximum bitrate feature, and the bitrate spikes too
much, you can try making the bitrate averaging window smaller. Oggenc
allows that with the switch "--advanced-encode-option
bitrate_average_window=X", where X is the window length in seconds.

Hope this helps,

Carsten Haese.

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