RTSP Server, SDP

When using network protocol SDP or RTSP, UltraGrid uses RTP as normally but 2 things act differently:

1. codecs are packed according to the RFCs (that however limits available codecs that can be used - H.264 for video and OPUS or PCMU for audio)
2. descriptive SDP file is produced - depending on the protocol used it is provided either as a file (or with a HTTP server) or utilized within a RTSP session

Note: Current implementation is able to handle only one receiver at the same time. To process multiple receivers, check Use Cases.

Table of Contents

• RTSP
• SDP
  • Multicast
• Supported formats
  • Audio
  • Video

RTSP

RTSP server can be run with following commands:

uv -t <your_capture> -c libavcodec:encoder=libx264 --video-protocol rtsp

or with audio

uv -t <your_capture> -c libavcodec:encoder=libx264 --video-protocol rtsp -s <audio_cap> --audio-codec u-law --audio-protocol rtsp

If you omit audio/video compression, some suitable will be chosen.

SDP

uv -t <video_capture> -s <audio_capture> --protocol sdp <receiver>

In this case, default compression will be chosen (can be changed similarly to RTSP, eg. also A-law or OPUS for audio). SDP file ug.sdp will be created which can then be played by the receiver given on command-line. Alternatively, the receiver can use (play) the URL provided by sender on terminal, eg.:

mplayer http://93.184.216.34:8554/ug.sdp

Multicast

UltraGrid can also use a multicast address as a receiver. In that case all receivers that are able to receive multicast can join the multicast group:

uv -t <video_capture> -s <audio_capture> --protocol sdp 224.0.0.20 # sender IPv4
uv -t <video_capture> -s <audio_capture> --protocol sdp ff02::20 # sender IPv6
mplayer http://93.184.216.34:8554/ug.sdp # receivers IPv4

Supported formats

Audio

• 1 channel PCMA/PCMU 8000 Hz (G.711) - --audio-codec u-law:sample-rate=8000
• 1 channel PCMA/PCMU or OPUS 48000 Hz
• 2 channel PCMA/PCMU 48000 Hz (--audio-codec u-law --audio-capture-format channels=2)

not working:

• OPUS with 2 or more channels

may be working:

• 1 channel OPUS with supported sampling rates (8, 12, 16, 24 and 48 kHz)
• multi-channel PCMA/PCMU with various sample rates

Video

Only H.264 is currently supported. For best compatibility it is recommended to turn of Intra Frame Refresh and possibly reduce the bitrate.