[Vorbis] Re: very low bandwidth encoding

[Andy Baxter]

On Wed, 22 Sep 2004 04:10:14 +1000, Geoff Shang wrote:

> Andy Baxter wrote:
> 
>> I'm trying to encode audio tracks as ogg vorbis at very low bandwidths for
>> peer to peer broadcasting. I.e. need to have two streams uploading from
>> modem users, which means the bitrate needs to be around 18-22 kbps.
> 
> Note that unless you're using modems with V.90, modems can only uplink at 
> 33.6 kbps, so you'll need a rate of less than 16 kbps if you want to be 
> able to up two at once.
> 
>> It's not easy to get good quality at this bitrate. The recipe I'm using at
>> the moment is:
>>
>> oggenc Mon-Sep-20-04-0\:3\:27.wav -b 20 -M 22 --resample 17000 --downmix
>> -o test.ogg
>>
>> which is OK, but still has a tinny sound with some tracks.
> 
> Not sure if you need to use --maanaged to get those constraints to take 
> effect.  But I'dve thought that something like -q -1 would be more 
> effective anyway. Any reason you've not gone with 16kHz?
> 
> Geoff.

-q 1 gives a bitrate of about 60 kbps. even -q -1 only goes down to about
30 in mono.

It looking now that the problem isn't with vorbis or the encoder so much
as the decoder - I've been using alsaplayer to play the tracks with, which
doesn't cope well with resampled oggs. 

oggenc -b 12 -M 18 --managed --resample 11025 --downmix
Wed-Sep-22-04-0\:1\:45.wav -o test-ogg-direct.ogg

is giving fairly decent sound at 12 kbps mono if I play it through ogg123,
but sounds tinny and strange if I play through alsaplayer. xmms has the
same problem. zinf plays these files OK - same as ogg123.

If you want ogg to be widely used, it might be a good idea to make sure
people writing the players have done it right; otherwise people are going
to be turned off by problems that are nothing to do with the format itself.

E.g. have a list somewhere of players / plugins that are recommended for
different platforms, and hassle the people who have written bad plugins to
do it right.

I've posted on the xmms-devel and alsaplayer-devel lists pointing out this
problem.

The same happens with most of the players I have installed - mplayer won't
play it at all; noatun and kaboodle have the same tinny sound as
alsaplayer. I think the problem is to do with the resampling - maybe these
players are using an internal upsampling algorithm that doesn't quite work
right.