Petter Reinholdtsen

Streaming the Linux desktop to Kodi using VLC and RTSP
12th July 2018

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}'

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Tags: debian, english, video.

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