webm dash manifest.

Question

I tried to create mpeg dash. here's my flow :

1. source.mp4 (UHD 4k) converted to 1080p, 720p ... 144p using following command:

   ffmpeg -i {source.mp4} -c:v libvpx-vp9 {size} -b:v 1500k -keyint_min 150 -tile-columns 4 -frame-parallel 1 -an -f webm -dash 1 {output.webm}

2. audio get splitted using:

   mpeg -i {source.mp4} -c copy {sound.m4a} then convert to webm using: mpeg -i {sound.m4a} -c:a libvorbis -b:a 128k -vn -f webm -dash 1 {audio.webm}

3 create manifest using :

ffmpeg \

-f webm_dash_manifest -i output-1080p.mp4 \
-f webm_dash_manifest -i output-720p.mp4 \
-f webm_dash_manifest -i output-480p.mp4 \
-f webm_dash_manifest -i output-360p.mp4 \
-f webm_dash_manifest -i output-240p.mp4 \
-f webm_dash_manifest -i output-144p.mp4 \
-f webm_dash_manifest -i audio.m4a \
-c copy -map 0 -map 1 -map 2 -map 3 -map 4 -map 5 -map 6 \
-f webm_dash_manifest \ 
-adaptation_sets "id=0,streams=0,1,2,3,4,5 id1,streams=6" {manifest.mpd}

the question is. why after step 3 manifest.mpd is empty, what should be the contain of manifest.mpd file?