I'm playing around with subsonic for a while now. Subsonic is a tomcat servlet which can stream your music collection to wherever you are. Nothing uncommon so far, but subsonic can very easily transcode media files on the fly. And this actually works.  At first I set it up to transcode to mp3 64kbit with lame. That turned out to be way too slow and was limited by the CPU (and not the bandwith) on my Duron 600 until I found the -f (fast) switch for lame.

The next thing which bothered me, was the sound quality. 64kbit CBR MP3 is not the best thing. So a good thing to do is using the --abr switch instead of just CBR. Using -m m (mono downmix) is also a good idea for such low bitrates.

A final transcoding command looks like this:

lame -S -f -m m --abr %b %s - 

Works pretty well. 

But you can go even further. OGG Vorbis is much better at lower bitrates then MP3. Since Subsonic doesn't have any particular knowledge about the media it streams it can also deliver ogg, the only thing you have to do is putting the appropriate transcoding lines into the transcoding table and activate them in the player config. There is one trap when setting up the transcoding/downsampling commands: oggenc cannot read .ogg files, but only .wav input. So the "downsampling command" doesn work, since you need to pipe oggdec and oggenc together, which are two commands. But you can set up a ogg>ogg transcoding command-set.

I use the following filters (optimized for low bandwith):

oggenc -Q --resample 22050 --downmix -b %b -o - %s 

lame -S --decode %s -

oggenc -Q --resample 22050 --downmix -b %b -

mppdec --wav --silent %s -

oggenc -Q --resample 22050 --downmix -b %b -

oggdec -Q %s -o -

oggenc -Q --resample 22050 --downmix -b %b -

note the last command-set which converts high-bitrate ogg to low-bitrate abr ogg