[vorbis] Mono wavs with b4

[Craig Dickson]

Moritz Grimm wrote:

> The last sentence means that you should halve those numbers yourself,
> because these values are the 6 modes for stereo input.
>
> I tried it on a mono file with 'oggenc -b 80 input.wav' and it worked
> fine - i got a mono .ogg with an ABR of 83kbit/s out of that.
>
> This really is confusing,

No kidding. It also means that you cannot simply apply the same parameters
to all files, mono and stereo, and expect comparable quality -- the 160k
mono files will be substantially better than 160k stereo.

I tried "oggenc -b 112 file.wav" with a mono file and was surprised to get a
file with an average bitrate of nearly 130k. Now it makes sense -- the
software translated my request for 112 to the same mode as 256k stereo, so I
actually got about 128k mono.

The "oggenc -h" help text is very unclear.

> I think it might be a good idea to give oggenc,
> in addition to the -b option, an option '-m' (for 'mode', just as an
> example and it's still unused, btw) followed by a number between 1 and 6
> and then let oggenc choose the appropriate bitrate for the input file.

Vorbis B2 had this! And I agree, it would be good to have it back.

> What I would not want is to replace the -b option. Being able to set the
> bitrate directly surely is useful from time to time.

Yes, absolutely.

> Assuming, the option '-m 2' (which should be default then, because -b
> 128 is default) gives a stereo_input.wav around 128kbit/s, it should
> give a mono_input.wav 64kbit/s, a 3channel_input.wav 192kbit/s, etc.

This makes sense to me.

Craig


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