Petter Reinholdtsen

If you read my blog regularly, you probably know I am involved in running and developing the Norwegian TV channel Frikanalen. It is an open channel, allowing everyone in Norway to publish videos on a TV channel with national coverage. You can think of it as Youtube for national television. In addition to distribution on RiksTV and Uninett, Frikanalen is also available as a Kodi addon. The last few days I have updated the code to add more features. A new and improved version 0.0.3 Frikanalen addon was just made available via the Kodi repositories. This new version include a option to browse videos by category, as well as free text search in the video archive. It will now also show the video duration in the video lists, which were missing earlier. A new and experimental link to the HD video stream currently being worked on is provided, for those that want to see what the CasparCG output look like. The alternative is the SD video stream, generated using MLT. CasparCG is controlled by our mltplayout server which instead of talking to mlt is giving PLAY instructions to the CasparCG server when it is time to start a new program.

By now, you are probably wondering what kind of content is being played on the channel. These days, it is filled with technical presentations like those from NUUG, Debconf, Makercon, and TED, but there are also some periods with EMPT TV and P7.

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I continue to explore my Kodi installation, and today I wanted to tell it to play a youtube URL I received in a chat, without having to insert search terms using the on-screen keyboard. After searching the web for API access to the Youtube plugin and testing a bit, I managed to find a recipe that worked. If you got a kodi instance with its API available from http://kodihost/jsonrpc, you can try the following to have check out a nice cover band.

curl --silent --header 'Content-Type: application/json' \
  --data-binary '{ "id": 1, "jsonrpc": "2.0", "method": "Player.Open",
  "params": {"item": { "file":
  "plugin://plugin.video.youtube/play/?video_id=LuRGVM9O0qg" } } }' \
  http://projector.local/jsonrpc

I've extended kodi-stream program to take a video source as its first argument. It can now handle direct video links, youtube links and 'desktop' to stream my desktop to Kodi. It is almost like a Chromecast. :)

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Last night, I wrote a recipe to stream a Linux desktop using VLC to a instance of Kodi. During the day I received valuable feedback, and thanks to the suggestions I have been able to rewrite the recipe into a much simpler approach requiring no setup at all. It is a single script that take care of it all.

This new script uses GStreamer instead of VLC to capture the desktop and stream it to Kodi. This fixed the video quality issue I saw initially. It further removes the need to add a m3u file on the Kodi machine, as it instead connects to the JSON-RPC API in Kodi and simply ask Kodi to play from the stream created using GStreamer. Streaming the desktop to Kodi now become trivial. Copy the script below, run it with the DNS name or IP address of the kodi server to stream to as the only argument, and watch your screen show up on the Kodi screen. Note, it depend on multicast on the local network, so if you need to stream outside the local network, the script must be modified. Also note, I have no idea if audio work, as I only care about the picture part.

#!/bin/sh
#
# Stream the Linux desktop view to Kodi.  See
# http://people.skolelinux.org/pere/blog/Streaming_the_Linux_desktop_to_Kodi_using_VLC_and_RTSP.html
# for backgorund information.

# Make sure the stream is stopped in Kodi and the gstreamer process is
# killed if something go wrong (for example if curl is unable to find the
# kodi server).  Do the same when interrupting this script.
kodicmd() {
    host="$1"
    cmd="$2"
    params="$3"
    curl --silent --header 'Content-Type: application/json' \
	 --data-binary "{ \"id\": 1, \"jsonrpc\": \"2.0\", \"method\": \"$cmd\", \"params\": $params }" \
	 "http://$host/jsonrpc"
}
cleanup() {
    if [ -n "$kodihost" ] ; then
	# Stop the playing when we end
	playerid=$(kodicmd "$kodihost" Player.GetActivePlayers "{}" |
			    jq .result[].playerid)
	kodicmd "$kodihost" Player.Stop "{ \"playerid\" : $playerid }" > /dev/null
    fi
    if [ "$gstpid" ] && kill -0 "$gstpid" >/dev/null 2>&1; then
	kill "$gstpid"
    fi
}
trap cleanup EXIT INT

if [ -n "$1" ]; then
    kodihost=$1
    shift
else
    kodihost=kodi.local
fi

mcast=239.255.0.1
mcastport=1234
mcastttl=1

pasrc=$(pactl list | grep -A2 'Source #' | grep 'Name: .*\.monitor$' | \
  cut -d" " -f2|head -1)
gst-launch-1.0 ximagesrc use-damage=0 ! video/x-raw,framerate=30/1 ! \
  videoconvert ! queue2 ! \
  x264enc bitrate=8000 speed-preset=superfast tune=zerolatency qp-min=30 \
  key-int-max=15 bframes=2 ! video/x-h264,profile=high ! queue2 ! \
  mpegtsmux alignment=7 name=mux ! rndbuffersize max=1316 min=1316 ! \
  udpsink host=$mcast port=$mcastport ttl-mc=$mcastttl auto-multicast=1 sync=0 \
  pulsesrc device=$pasrc ! audioconvert ! queue2 ! avenc_aac ! queue2 ! mux. \
  > /dev/null 2>&1 &
gstpid=$!

# Give stream a second to get going
sleep 1

# Ask kodi to start streaming using its JSON-RPC API
kodicmd "$kodihost" Player.Open \
	"{\"item\": { \"file\": \"udp://@$mcast:$mcastport\" } }" > /dev/null

# wait for gst to end
wait "$gstpid"

I hope you find the approach useful. I know I do.

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PS: See the followup post for a even better approach.

A while back, I was asked by a friend how to stream the desktop to my projector connected to Kodi. I sadly had to admit that I had no idea, as it was a task I never had tried. Since then, I have been looking for a way to do so, preferable without much extra software to install on either side. Today I found a way that seem to kind of work. Not great, but it is a start.

I had a look at several approaches, for example using uPnP DLNA as described in 2011, but it required a uPnP server, fuse and local storage enough to store the stream locally. This is not going to work well for me, lacking enough free space, and it would impossible for my friend to get working.

Next, it occurred to me that perhaps I could use VLC to create a video stream that Kodi could play. Preferably using broadcast/multicast, to avoid having to change any setup on the Kodi side when starting such stream. Unfortunately, the only recipe I could find using multicast used the rtp protocol, and this protocol seem to not be supported by Kodi.

On the other hand, the rtsp protocol is working! Unfortunately I have to specify the IP address of the streaming machine in both the sending command and the file on the Kodi server. But it is showing my desktop, and thus allow us to have a shared look on the big screen at the programs I work on.

I did not spend much time investigating codeces. I combined the rtp and rtsp recipes from the VLC Streaming HowTo/Command Line Examples, and was able to get this working on the desktop/streaming end.

vlc screen:// --sout \
  '#transcode{vcodec=mp4v,acodec=mpga,vb=800,ab=128}:rtp{dst=projector.local,port=1234,sdp=rtsp://192.168.11.4:8080/test.sdp}'

I ssh-ed into my Kodi box and created a file like this with the same IP address:

echo rtsp://192.168.11.4:8080/test.sdp \
  > /storage/videos/screenstream.m3u

Note the 192.168.11.4 IP address is my desktops IP address. As far as I can tell the IP must be hardcoded for this to work. In other words, if someone elses machine is going to do the steaming, you have to update screenstream.m3u on the Kodi machine and adjust the vlc recipe. To get started, locate the file in Kodi and select the m3u file while the VLC stream is running. The desktop then show up in my big screen. :)

When using the same technique to stream a video file with audio, the audio quality is really bad. No idea if the problem is package loss or bad parameters for the transcode. I do not know VLC nor Kodi enough to tell.

Update 2018-07-12: Johannes Schauer send me a few succestions and reminded me about an important step. The "screen:" input source is only available once the vlc-plugin-access-extra package is installed on Debian. Without it, you will see this error message: "VLC is unable to open the MRL 'screen://'. Check the log for details." He further found that it is possible to drop some parts of the VLC command line to reduce the amount of hardcoded information. It is also useful to consider using cvlc to avoid having the VLC window in the desktop view. In sum, this give us this command line on the source end

cvlc screen:// --sout \
  '#transcode{vcodec=mp4v,acodec=mpga,vb=800,ab=128}:rtp{sdp=rtsp://:8080/}'

and this on the Kodi end

echo rtsp://192.168.11.4:8080/ \
  > /storage/videos/screenstream.m3u

Still bad image quality, though. But I did discover that streaming a DVD using dvdsimple:///dev/dvd as the source had excellent video and audio quality, so I guess the issue is in the input or transcoding parts, not the rtsp part. I've tried to change the vb and ab parameters to use more bandwidth, but it did not make a difference.

I further received a suggestion from Einar Haraldseid to try using gstreamer instead of VLC, and this proved to work great! He also provided me with the trick to get Kodi to use a multicast stream as its source. By using this monstrous oneliner, I can stream my desktop with good video quality in reasonable framerate to the 239.255.0.1 multicast address on port 1234:

gst-launch-1.0 ximagesrc use-damage=0 ! video/x-raw,framerate=30/1 ! \
  videoconvert ! queue2 ! \
  x264enc bitrate=8000 speed-preset=superfast tune=zerolatency qp-min=30 \
  key-int-max=15 bframes=2 ! video/x-h264,profile=high ! queue2 ! \
  mpegtsmux alignment=7 name=mux ! rndbuffersize max=1316 min=1316 ! \
  udpsink host=239.255.0.1 port=1234 ttl-mc=1 auto-multicast=1 sync=0 \
  pulsesrc device=$(pactl list | grep -A2 'Source #' | \
    grep 'Name: .*\.monitor$' |  cut -d" " -f2|head -1) ! \
  audioconvert ! queue2 ! avenc_aac ! queue2 ! mux.

and this on the Kodi end

echo udp://@239.255.0.1:1234 \
  > /storage/videos/screenstream.m3u

Note the trick to pick a valid pulseaudio source. It might not pick the one you need. This approach will of course lead to trouble if more than one source uses the same multicast port and address. Note the ttl-mc=1 setting, which limit the multicast packages to the local network. If the value is increased, your screen will be broadcasted further, one network "hop" for each increase (read up on multicast to learn more. :)!

Having cracked how to get Kodi to receive multicast streams, I could use this VLC command to stream to the same multicast address. The image quality is way better than the rtsp approach, but gstreamer seem to be doing a better job.

cvlc screen:// --sout '#transcode{vcodec=mp4v,acodec=mpga,vb=800,ab=128}:rtp{mux=ts,dst=239.255.0.1,port=1234,sdp=sap}'

As usual, if you use Bitcoin and want to show your support of my activities, please send Bitcoin donations to my address 15oWEoG9dUPovwmUL9KWAnYRtNJEkP1u1b.