[H-GEN] Re: converting from speex to ogg vorbis

[Geoff Shang]

Byron Ellacott wrote:

> Clinton Roy wrote:
>> speexdec --stereo foo.spx foo.wav
>> oggenc foo.wav
>> Like the problem, the solution does'nt make any sense, enlightenment
>> appreciated :)

I don't think Clinton was looking for a tutorial on digital audio.  His 
point was that he had to force speexdec to decode to stereo before encoding 
with oggenc would produce a usable file.  since the file parameters should 
be stored in the wav header, forcing it to decode to stereo should not have 
affected the functionality, only the audio produced.

> Dolby 5.1 refers to 5.1 
> channels: front left, front right, rear left, rear right, bass and center. 
> The center is the point one.  I don't know how Dolby audio is encoded, 
> though.

Actually, the bass, also known as the LFE or subwoofer channel, is the 
point 1.

Dolby Digital audio is encoded using Dolby's AC-3 codec.  this is a lossy 
codec, like MP3 or Ogg Vorbis.  Its distinguishing feature, at least from 
MP3, is that it is multi-channel.  http://www.dolby.com/tech/multipc.html

Dolby Digital 5.1 mixes are generally encoded on DVD at 448 kbps or 384 
kbps.  2.0 channel mixes (i.e. stereo soundtracks) are usually at 192 kbps. 
I have seen the odd one at 224 kbps, and a couple at 96 kbps (mainly for 
commentaries).  AC-3 is supposed to be able to go as low as 32 
kbps/channel, but given its lowest sampling rate is 32 kHz, I dare say it'd 
be pretty artifacty at that rate.

Note that Ogg Vorbis is technically capable of encoding up to 256 channels. 
there are few tools able to encode multi-channel Ogg Vorbis files though (I 
believe oggenc will do it if you hand it the right data), and there is no 
channel coupling as yet for the additional channels.

Geoff.