MarconiNet Project

Tools

Transmitter

The transmitter creates a single multicast stream from one or more of the following sources:

• local audio input (microphone, CD player, ...);
• external unicast or multicast streams, converted to an audio stream;
• possibly a sound file, for commercials;
• possibly an rtpdump file, for commercials;

NeVoT allows to do all but the last of these, but needs to be compiled/ported to Linux and outfitted with higher-quality codecs (MPEG L2/L3, DVI for sampling rates above 8 kHz).

It should be able to announce the current music title or, for example, a URL during a commercial, probably as an RTCP SDES NOTE item or as an additional SDES item. When playing from a file, that information is already typically contained in the sound file header.

This transmitter can be used for both the "network" station and local affiliates, either in "retransmission" or "insertion" mode.

Announcer

The announcer allows to distribute program announcements, at the channel level.

Can probably use SDR, multikit or the Precept tool for that initially. There are also existing non-GUI tools. Might want to enhance this with the ability to announce the location of where an on-demand version of the broadcast can be found.

Recorder/media server (RTSP)

The recorder records RTP streams and plays them back on request, using RTSP. Files are stored as rtpdump or RealAudio (.ra) files. A separate utility can then extract the RTCP NOTE entries from the stored file and create a playlist with RTSP URLs that allow random access to parts of the program.

There is existing, local work (currently, LiYong Yiet) on creating an RTSP server for recording and playback. It needs to be completed. There is also on-going work (Alex Basile) for a simple Java-based RTSP client, but the outcome is uncertain.

Issues

• How to blend commercials and program material?
• How does the "network" station (CBS, NBC, in the current world) signal to the "affiliates" when to play local material? (An out-of-band, encrypted packet stream indicating timestamps or NTP time would probably work, but need to worry about reliability.)
• "Insertion" mode only works if different local affiliates have non-overlapping multicast reach, as otherwise, a receiver would get advertising from both sources. (This can be dealt with at the receiver, but is probably best avoided.)