[vorbis-dev] Accessing lower bitrates?

[Michael Smith]

At 03:40 PM 7/22/02 -0700, you wrote:
>Throughout the website there is mention of vorbis supporting very low 
>bitrates (down to 8kbps mono) but the lowest I am able to get the encoder 
>library to go is roughly 24kbits, which I get to by handing in an 11 kHz 
>mono wav into the encoder and asking it for a 16 kbit bitrate (asking for 8 
>kbits fails):
>
>ret = (vorbis_encode_setup_managed(&vi,1,sample_rate,-1,bitrate,-1) ||
>            vorbis_encode_ctl(&vi,OV_ECTL_RATEMANAGE_AVG,NULL) ||
>            vorbis_encode_setup_init(&vi));
>
>A 2-second input file yields a 6.5kByte file, which is 6.5/2 * 8 = 26kbit/sec
>
>How do I get the encoder to go even lower?  I'd really like to explore the 
>absolute bottom of the available bitrates.

Vorbis has large headers (~4 kB) at the start of each stream, so you get
way off bitrate numbers if you use 2 second input files. So don't do that
if you want to really see the actual audio data bitrate. (most encoders
and decoders will tell you the bitrate NOT including the headers - oggenc
does, for example).

Michael

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