This is an experimental implementation of Wi-Fi Display (aka Miracast).

The application will stream the selected monitor if the mutter screencast portal is available. If it is unavailable, a fallback to X11 based frame grabbing will happen. As such, it should work fine in almost all setups.

To get audio streaming, you need to change the audio output in pulseaudio to use the created "Network-Displays" sink.

To use it, you will need:

• openh264 or x264
• For audio supporting using AAC one of fdkaacenc, faac or avenc_aac
• NetworkManager version > 1.15.2

Build

To build it locally:

• clone the repository
• install meson
• run meson build on the cloned repository
• run meson install on the build folder created by meson

Devices

The following devices have been tested:

• Measy "Miracast Receiver" Model A2W
  • Announces itself as EZMirror/EZCast
  • Only supports uncompressed audio (LPCM) which is not supported yet
• LG WebOS TV
• MontoView (Software Revision 2.18.02)
• MiraScreen

Testing

For testing purposes you can run with NETWORK_DISPLAYS_DUMMY=1 set. In that case, a dummy sink will be provided that allows connecting on localhost using any RTSP capable client to test WFD streaming.

You can connect to rtsp://localhost:7236/wfd1.0 then.

Debugging

Codecs

Appropriate video/audio encoders will be selected automatically. You should also get a notification if codecs are missing and an offer to automatically install these. To debug the codecs themselves, you can modify the default choice by setting the NETWORK_DISPLAYS_H264_ENC and NETWORK_DISPLAYS_AAC_ENC environment variables and specifying the gstreamer element to use (if supported and detected). Run with G_MESSAGES_DEBUG=all to see the selection at work during connection establishment.

Connection issues

P2P WiFi/WiFi Direct and the mechanism to establish a connection is a relatively complicated process that can fail in a number of different ways and stages.

As a first step, you should run with G_MESSAGES_DEBUG=all to get a better idea when the failure happens. Your TV/Display may also give an indication about the progress. Much of the information is also displayed in the UI, but might only be visible for a very short period of time.

Discovery

The first required step is successful discovery of the remote device. This step can already be problematic sometimes. Confirm the following, each ensuring that support exists:

• Run gnome-network-displays with G_MESSAGES_DEBUG=all. This will print a lot more information. Theoretically it may be that we see the device, but think that it is not WiFi Display capable (e.g. because the wpa_supplicant support is missing, see further below). Look out for the following messages:

  • WFDP2PRegistry: Got NMClient: The connection to NetworkManager works.
  • WFDP2PRegistry: Found a new device, creating provider: This means that we have a seemingly usable P2P device installed.
  • WFDP2PProvider: Ignoring peer "XX:XX:XX:XX:XX" (Y) as it has no WFDIEs set: This means there is a P2P device, but it does not seem to support WiFi Display. It may also mean that wpa_supplicant is not complied with the required support, see below.
  • WFDP2PProvider: Found a new sink with peer X on device Y: The device has been found, everything should be good.

• nmcli device shows your WiFi device and a corresponding p2p-dev-X device. If you do not see your WiFi device, then NetworkManager is probably not managing it for some reason. Both the main WiFi device and the P2P device need to be managed by NetworkManager.

• iw dev should show an Unnamed/non-netdev interface device with type P2P-device.

  If this is not the case, then the device is likely unsupported. One example of this are legacy wext drivers, which may support P2P operation, but are not (and will not be) supported by this software.

• NetworkManager only support P2P operation together with wpa_supplicant. The use of iwd is currently not supported and you may have enabled it in NetworkManager.

• If NetworkManager does not even show a device, then, as root, run

  gdbus call --system --dest fi.w1.wpa_supplicant1 --object-path /fi/w1/wpa_supplicant1 --method org.freedesktop.DBus.Properties.Get fi.w1.wpa_supplicant1 Capabilities
  

  This should output something like (<['ap', 'ibss-rsn', 'p2p', 'pmf', 'mesh', 'ft', 'sha384']>,). Make sure that p2p is listed here. If it is not, then wpa_supplicant was compiled without P2P WiFi support (CONFIG_P2P).

• If a device is shown, but it does not work, then, as root, run

  gdbus call --system --dest fi.w1.wpa_supplicant1 --object-path /fi/w1/wpa_supplicant1 --method org.freedesktop.DBus.Properties.Get fi.w1.wpa_supplicant1 WFDIEs
  

  If this runs successfully, it'll return (<@ay []>,). This answer will be longer when we try to connect to a device, but only at that point. If it shows an error, then your wpa_supplicant was compiled without WiFi Display support (CONFIG_WIFI_DISPLAY).

If everything looks good, but you still can't find the TV, then please try the following:

• Search for it using another device at the same time.
• Try running

  gdbus call --system --dest fi.w1.wpa_supplicant1 --object-path /fi/w1/wpa_supplicant1 --method org.freedesktop.DBus.Properties.Set fi.w1.wpa_supplicant1 WFDIEs "<@ay [0x00, 0x00, 0x06, 0x00, 0x90, 0x1c, 0x44, 0x00, 0xc8]>"
  

  Doing this will set the WFD Information Elements earlier in the process. It should not make a difference. But if it does, then some bigger changes will be needed.
• If you can, try to get a capture of another device discovering it.

  iw phy phyX interface add mon0 type monitor
  ip link set mon0 up
  

  Then connect to it using wireshark. You may need to disable your normal WiFi connection and change the channel using iw dev. Explaining the details is out of scope for this document.

Establishing a P2P Group

When you click on the TV, the first step is to establish a WiFi P2P connection. Check whether you see the message:

Got state change notification from streaming sink to state ND_SINK_STATE_WAIT_P2P
[...]
Got state change notification from streaming sink to state ND_SINK_STATE_WAIT_SOCKET

If you see both of these messages, then we have successfully created a P2P Group.

Network configuration and socket connection

What happens next is that both side will configure their network. Then the TV will establish a connection to gnome-network-displays.

Things could go wrong here:

• Usually, NetworkManager will set up the network to be shared using dnsmasq
• A local firewall might block DHCP requests/responses or prevent the later connection

At this point the IP link is there. You can do the following:

• Look into the NetworkManager log whether you see something obviously wrong (unlikely, as otherwise it should disconnect immediately).

• The low level link is established (i.e. a P2P network device has been created). This means, to debug further, we can montior this network device and see what is happening. We should see a DHCP handshake to configure the network, and then an attempt to establish an RTSP connection.

  The easiest way to do this is to have wireshark running. Then, right after clicking on the TV, the P2P device will show up in the list. Quickly start a capture on it.

  Alternatively, use a script like the following (as root):

  interface=""; while [ -z "$interface" ]; do interface=$( ls /sys/class/net/ | grep -- p2p- ); sleep 0.1; done; echo $interface; tcpdump -i "$interface" -w /tmp/p2p-connection-dump.pcap
  

  And then open the created dump file /tmp/p2p-connection-dump.pcap in Wireshark.

RTSP stream issues

Not all devices are compliant, and the standard is a bit odd. If you have problems where the stream seems to start, but then does not work or stop after a while.

Try the following:

• Run with G_MESSAGES_DEBUG=all and check if you see something that is wrong. Note that certain warnings are expected.
• Try grabbing a tcpdump/wireshark capture (see above) and check whether you see something weird in the RTSP stream.
• It could also be an issue with the GStreamer pipeline not starting properly. This can possibly be debugged using e.g. GST_DEBUG=*:5, but is generally harder to pin point. Try it a few times, and check if the problem persists.