Output stream only have one Representation (one video) in AdaptationSet of DASH if use ffmpeg rtmp sending the Xcode stream to Nignix server for Dash segment.

[wangjingz]

Describe the bug
Output stream of CDN-Transcoding sample only have one Representation (one video) in AdaptationSet of DASH if use ffmpeg rtmp sending the stream to Nginx server for Dash segment.

To Reproduce

1. complete 1toN transcoding with Nignx docker setup according to readme.
   start 1: xeon-ubuntu1804-ffmpeg:1.0 docker to complete transcoding task.
   start 2: xeon-ubuntu1804-nginx-rtmp:1.0 docker to complete Dash segment.

2. input streaming as:
   root@f1ac23ac6f74:/media/_System_Validation# ffmpeg -re -i /media/_System_Validation/mp4_h264aac/h264_1920x1080_b@40_2397_8225kbps_cbr_aac_lc_256kbps_48000_hd_the_living_see_2mn48s.mp4 -c:v copy -f flv rtmp://192.168.31.32/stream/xcode

3. Xcode server to do transcoding and rtmp upstreaming to nginx server:
   transcoding (xeon-ubuntu1804-ffmpeg:1.0 docker) -> DASH segement MPD file (xeon-ubuntu1804-nginx-rtmp:1.0 docker )
   command as:
   ffmpeg -i rtmp://192.168.31.32/stream/xcode -c:a copy -c:v libsvt_hevc -f flv rtmp://192.168.31.31/dash/hevc

4. only have one video in MPD file. (xeon-ubuntu1804-nginx-rtmp:1.0 docker )
   only one stream is supported in flv format.

Expected behavior
need multi-video in DASH MPD with different resolution and bitrate to adapt different network situation.
Additional context
just link use ffmpeg command line to achieve multi-video :

root@1fb8d4cd2580:/media/dash# ffmpeg -i rtmp://192.168.31.32/stream/xcode -filter_complex 'split=2[s0][s1];[s0]scale=480:-2[480s];[s1]scale=1080:-2[1080s]' -map '[480s]' -c:v:0 libsvt_hevc -map '[1080s]' -c:v:1 libsvt_hevc -map a -c:a:0 copy -ar:a:0 22050 -map a -c:a:1 copy -ar:a:1 44100 -g 150 -sc_threshold 0 -b_strategy 0 -min_seg_duration 5000 -use_timeline 0 -use_template 1 -single_file 1 -window_size 5 -adaptation_sets "id=0,streams=v id=1,streams=a" -f dash /media/dash/hevc_audiocopy.mpd 

[TangZhiZhen]

this issue is duplicated with #10
the #26 is merged and close this issue