Videoconferencing Mode

UltraGrid allows for multipoint video and audio distribution in a videoconferencing mode. In such a case UltraGrid acts as a mixer. Audio and video mixers are separate in UltraGrid.

For the video UltraGrid scales and composes the incoming video streams in a specified layout and sends the resulting video stream to given hosts or IPs. It is possible to specify different video compressions and stream parameters for individual target hosts in the same way as with the reflector (see Reflector settings for reference).

Audio is mixed using linear (or logarithmic) audio mixer and the audio is sent back to all source hosts. For each host its own source audio is omitted from the resulting audio mix.

See also Multipoint Setup if you want to omit mixing and run the multipoint directly. This is usually only suitable for few parties (3-4) otherwise it is rather complex to setup provided that it should be a full mesh setup.

Table of Contents

• Video Mixer
• Audio Mixer
• Example Use Case
• See also

Video Mixer

Note: Videoconference must be compiled-in. If not, check Compile UltraGrid (Source)#Conference. You can verify presence of the module with following command:

uv -d help | grep conference

To start the video mixer run:

hd-rum-transcode --conference <width>:<height>:<fps> 8M 5004 <host1_opts> <host1> \
    <host2_opts> <host2> ... <hostn_opts> <hostn>

Sample usage is:

hd-rum-transcode -conference 1920:1080:30 8M 5004 -c libavcodec:codec=H.264:bitrate=10M receiver1 \
    receiver2 -c JPEG receiver3

Notes:

1. If you want to run the mixer on a machine that is part of the conference, change RX video any unused port, eg. 5008:

   nodeX$ uv -d gl -t <vcapture> -P 5008:5004
   

   for the UltraGrid instance that is part of the conference (not the mixer) and use that port with the mixer for this particular host:

   nodeX$ hd-rum-transcode -conference 1920:1080:30 8M 5004 -c libavcodec:codec=H.264:bitrate=10M nodeY \
       -P 5008 localhost
   

Audio Mixer

To start the audio mixer run:

uv -r mixer:algo=linear

The general usage of the audio mixer is as follows:

uv -r mixer[:codec=<codec>][:algo={linear|logarithmic}]

<codec>
	audio codec to use
linear
	linear sum of signals (with clamping)
logarithmic
	linear sum of signals to threshold, above threshold logarithmic dynamic range compression is used

Notes:

1. You do not need to specify audio participants explicitly, UltraGrid simply sends the the stream back to the host that is sending to mixer. Therefore it is necessary to use single UltraGrid instance for both sending and receiving audio.

2. Mixer uses default port for receiving, therefore if you want to use it on machine that is a part of the conference, you must change the default audio RX port, eg. to 5010:

   uv -s <acapture> -r <aplayback> -P 5004:5004:5010:5006

   for the UltraGrid instance that is part of the conference (not the mixer!).

3. you can use --param low-latency-audio to improve the latency (but double check if the audio is stable in this case)

Example Use Case

In this use case will be presented case with 3 parties A, B and C. Mixers will be running on A - without that it will be easier because you won't need to fiddle with ports:

A$ uv -t testcard -s testcard -d gl -r alsa -c libavcodec --audio-codec OPUS -P 5008:5004:5010:5006 localhost
A$ uv -r mixer:codec=OPUS
A$ hd-rum-transcode -conference 1920:1080:30 8M 5004 -c libavcodec:codec=H.264:bitrate=10M B C -P 5008 localhost
B$ uv -t testcard -s testcard -d gl -r alsa -c libavcodec --audio-codec OPUS A
C$ uv -t testcard -s testcard -d gl -r alsa -c libavcodec --audio-codec OPUS A

If there is a separate host M that mixes the streams, commands will be:

A$ uv -t testcard -s testcard -d gl -r alsa -c libavcodec --audio-codec OPUS M
B$ uv -t testcard -s testcard -d gl -r alsa -c libavcodec --audio-codec OPUS M
C$ uv -t testcard -s testcard -d gl -r alsa -c libavcodec --audio-codec OPUS M
M$ uv -r mixer:codec=OPUS
M$ hd-rum-transcode -conference 1920:1080:30 8M 5004 -c libavcodec:codec=H.264:bitrate=10M A B C

See also

• Multipoint Setup