You could lame to decode with a pipe, ie. LAME -m mono --decode input.mp3 - | oggenc -whateveroptionsyouwant -input - -output file.ogg
Note that i made up the parameters for oggenc, cos i've never used it, so find out what options you need to do mono encoding with stdin as the input file (usually done by specifying '-' as the file name), Also I don't know if the -m mono switch works for decoding, but that shouldnt matter if you can get oggenc to do the mono conversion, or if the input mp3 is already mono.
Thank for replying. I'm using this on Windows XP and I don't know if the pipe it working.
Whatever oggenc - parameters I use, I always end up with a 1.mp3.wav file on my harddisc
(for which I do not have the harddisc space in real life)
The lame help also specifies the "--decode" option as
" --decode input=mp3 file, output=wav"
C:\Temp\3>lame -m mono --decode 1.mp3 | oggenc2 -input - --output=file.ogg
ID3v2 found. Be aware that the ID3 tag is currently lost when transcoding.
input: 1.mp3 (44.1 kHz, 2 channels, MPEG-1 Layer III)
output: 1.mp3.wav (16 bit, Microsoft WAVE)
skipping initial 1105 samples (encoder+decoder delay)
Frame# 12/10694 192 kbps MS oggenc2: invalid option -- i
Frame# 13/10694 160 kbpsWARNING: Unknown option specified, ignoring->
Frame# 10694/10694 32 kbps MS
ERROR: Input file "(stdin)" is not a supported format