[FFmpeg-user] How to convert 48000/2/FLOATLE AC3 to 48000/2/S16LE MP3

[Rene Herman]

Good day.

I have a (M2TS) input stream with floatle AC3 audio:

=== (mplayer)
Opening audio decoder: [ffmpeg] FFmpeg/libavcodec audio decoders
AUDIO: 48000 Hz, 2 ch, floatle, 640.0 kbit/20.83% (ratio: 80000->384000)
Selected audio codec: [ffac3] afm: ffmpeg (FFmpeg AC-3)
===

which I wish to transcode to s16le MP3 audio. I have by now tried 
probably a few hundred ways of writing:

$ ffmpeg -i "$SRC" -c:v mpeg4 -vtag xvid -vf 
crop=1280:550:0:$(((720-550)/2+2)),scale=640:-1 -b:v 900k -c:a 
libmp3lame -af aformat=s16 -b:a 128k -map_metadata -1 "$DST"

... but every such attempt (which didn't bomb out due to bad parameter 
syntax to start with) has still resulted in floatle MP3:

=== (mplayer)
Opening audio decoder: [ffmpeg] FFmpeg/libavcodec audio decoders
AUDIO: 48000 Hz, 2 ch, floatle, 128.0 kbit/4.17% (ratio: 16000->384000)
Selected audio codec: [ffmp3float] afm: ffmpeg (FFmpeg MPEG layer-3 audio)
===

I'm using ffmpeg 2.0.1 on arch linux. Would anyone know how this can be 
achieved?

Regards,
Rene.