What about DAB radio?

[vale-max]

Hi @rern ,
another idea for a feature to add to rAudio, DAB radio reproduction.

I already use my installation of rAudio to listen to DAB radios using an inexpensive RTL SDR dongle (around 20€) and open source software dab-cmdline

On a Raspberry Pi4 with 2Gb RAM it works perfectly.
I can contribute factively sending you an SDR dongle if you want to check the feasibility.

[vale-max]

Hello @rern
I did some experiment on how to add DAB radios to rAudio.
There is this appropriately named rtsp-simple-server which can be easily configured to start a program that can publish a stream on-demand.

Thus I changed a bit the format of the dab-scanner util from dab-cmdline and created a wrapper script that for every DAB audio service that has been found:
adds a service stanza in the rtsp-simple-server.yml which can launch the dab receiver and publish on the given URL
creates a file in /srv/http/data/webradios that can trigger the server

There are two issues in this moment that I haven't fixed yet:

1. the command that publish the stream is not stopped automatically.
   it seems piping the output of one command to the other makes them "deaf" to SIGINT
   Probably it can be fixed with a wrapper script using named pipes

2. To publish it as rtsp I can't use the PCM coming from the dab decoder, so I need to have the stream reencoded as AAC, which is wrong in many ways, first because is a waste of CPU cycles, then because AAC is a lossy format, also because the DAB stream is natively AAC so it seems stupid to decode/reencode it.
   However the native DAB stream uses a frame length which is not implemented by ffmpeg so I need to have it decoded to raw PCM by the dab receiver program and reencode it to be streamed.

I haven't found an easy way to pass it to MPD in a lossless format, and the alternative to have it played directly by one of the dab-cmdline examples is ugly as that way MPD would be totally unaware of what is playing.

Any idea, if you are interested in adding this feature, is welcome.

This is my script to add the services, the modified dab-scanner to create the services list in the required format is in my fork of dab-cmdline git:

#!/bin/bash
RADIO_LIST="/root/dabradios.txt"
BASE_YML="/root/rtsp-simple-server.yml_start"
NEW_YML="/root/rtsp-simple-server.yml"
#this is needed to consider the lowercase accented chars outside of "alnum"
LC_CTYPE=C

trim() {
    local var="$*"
    var="${var%"${var##*[![:space:]]}"}"   
    printf '%s' "$var"
}

readarray -t services < $RADIO_LIST
cp $BASE_YML $NEW_YML
rm -f /srv/http/data/webradios/rtsp\:\|\|localhost\:8554*
for service in "${services[@]}"; do
   if grep -q "^audioservice" <<< $service; then
      readarray -d ';' -t field <<< $service
      service_name=$(trim "${field[1]}")
      service_chan=$(trim "${field[2]}")
      legal_name=${service_name//[^[:alnum:]]/_}
cat <<EOT >>$NEW_YML
  $legal_name:
    runOnDemand: dab-rtlsdr-3 -P "$service_name" -C $service_chan|ffmpeg -re -ar 48000 -ac 2 -f s16le  -i - -vn -c:a aac -b:a 160k -f rtsp rtsp://localhost:\$RTSP_PORT/\$RTSP_PATH
    runOnDemandRestart: yes
    runOnDemandStartTimeout: 10s
    runOnDemandCloseAfter: 10s
EOT
echo "DAB $service_name" >/srv/http/data/webradios/rtsp\:\|\|localhost\:8554\|$legal_name

echo done for $legal_name
   fi
done