I get the same problem on Sarge - This is the tail of the problem, video streams fine - but no audio - please help!
[00000206] stream_out_transcode private debug: creating video transcoding from fcc=`mp4v' to fcc=`DIV3'
[00000247] main decoder debug: looking for decoder module
[00000247] main decoder debug: probing 17 candidates
[00000247] ffmpeg decoder debug: libavcodec initialized (interface 4748 )
[00000247] ffmpeg decoder debug: postprocessing disabled
[00000247] ffmpeg decoder debug: using direct rendering
[00000247] ffmpeg decoder debug: ffmpeg codec (MPEG-4 Video) started
[00000012] main module debug: using decoder module "ffmpeg"
[00000248] main encoder debug: looking for encoder module
[00000248] main encoder debug: probing 4 candidates
[00000248] ffmpeg encoder debug: libavcodec already initialized
[00000248] ffmpeg encoder debug: found encoder MS MPEG-4 Video v3
[00000014] main module debug: using encoder module "ffmpeg"
[00000014] main module debug: unlocking module "ffmpeg"
[00000248] main encoder debug: looking for encoder module
[00000248] main encoder debug: probing 4 candidates
[00000248] ffmpeg encoder debug: libavcodec already initialized
[00000248] ffmpeg encoder debug: found encoder MS MPEG-4 Video v3
[00000014] main module debug: using encoder module "ffmpeg"
[00000215] main private debug: adding a new input
[00000215] mux_asf private debug: adding input
[00000243] mpeg_audio packetizer: MPGA channels:2 samplerate:44100 bitrate:128
[00000205] main stream output debug: adding a new input
[00000206] stream_out_transcode private debug: creating audio transcoding from fcc=`mpga' to fcc=`mp3 '
[00000257] main decoder debug: looking for decoder module
[00000257] main decoder debug: probing 17 candidates
[00000072] main module debug: using decoder module "mpeg_audio"
[00000258] main encoder debug: looking for encoder module
[00000258] main encoder debug: probing 4 candidates
[00000258] ffmpeg encoder debug: libavcodec already initialized
[00000258] ffmpeg encoder debug: found encoder MPEG Audio layer 1/2/3
[00000014] main module debug: using encoder module "ffmpeg"
[00000259] main private debug: looking for audio filter2 module
[00000259] main private debug: probing 1 candidate
[00000206] stream_out_transcode private debug: no audio filter found ( -> )
[00000072] main module debug: unlocking module "mpeg_audio"
[00000014] main module debug: unlocking module "ffmpeg"
[00000206] stream_out_transcode private error: cannot create audio chain
[00000243] main packetizer error: cannot create packetizer output