Please help: This ffmpeg command won't convert AND copy/passthru audio

[mp4_guy]

I want to convert this source MP4 video containing AC3 5.1 audio to stereo, but also copy (passthru) the same audio stream as a secondary soundtrack in the output file.

ffmpeg -i SOURCE.MP4 -map 0:v -c:v copy -map 0:a -c:a:0 mp3 -ac:a:0 2 -filter_complex "[0:a:0]aresample=matrix_encoding=dplii" -map 0:a -c:a:1 copy OUTPUT.MP4

The result is a video with ONE audio stream: just the converted mp3, and it ignores the audio "copy" command to create a secondary soundtrack: the untouched AC3 5.1 audio. (I know Handbrake does this flawlessly, but I don't want to re-encode the video stream which Handbrake requires).

Any help would be appreciated.

[JVRaines]

Create two inputs to the same file:

ffmpeg -i SOURCE.MP4 -i SOURCE.MP4 -map 0:v -c:v copy -map 0:a -c:a:0 mp3 -ac:a:0 2 -filter_complex "[0:a:0]aresample=matrix_encoding=dplii" -map 1:a -c:a:1 copy OUTPUT.MP4

[pandy]

I modified one of my scripts - not tested but should work, audio track is copied and at the same time stereo version with small dynamics compression and level normalization encoded as mp3 and added as second audio track

ffmpeg.exe -i source.mp4 -map 0:v -c:v copy -map 0:a -c:a:0 copy -filter_complex "[0:a:0]pan=stereo|FL < FL + 1.414FC + .5BL + .5SL + .25LFE + .125BR|FR < FR + 1.414FC + .5BR + .5SR + .25LFE + .125BL,dynaudnorm=p=1/sqrt(2):m=100:s=10,firequalizer=gain='if(gte(f,42),0,-INF)+if(lte(f,13749),0,-INF)':accuracy=1:fixed=on:delay=0.05,asetpts=PTS-0.05/TB[a2c]" -map [a2c]:1 -c:a:1 libmp3lame -q:a:1 6 -map 0:s -c:s copy -f matroska source.mkv