LibreTime supports direct connection to two popular streaming media servers, the open source Icecast (http://www.icecast.org) and the proprietary SHOUTcast (http://www.shoutcast.com). Apart from the software license, the main difference between these two servers is that Icecast supports simultaneous MP3, AAC, Ogg Vorbis or Ogg Opus streaming from LibreTime, whereas SHOUTcast supports MP3 and AAC streams but not Ogg Vorbis or Opus. The royalty-free Ogg Vorbis format has the advantage of better sound quality than MP3 at lower bitrates, which has a direct impact on the amount of bandwidth that your station will require to serve the same number of listeners. Ogg Opus also benefits from good sound quality at low bitrates, with the added advantage of lower latency than other streaming formats. Opus is now an IETF standard (http://tools.ietf.org/html/rfc6716) and requires Icecast 2.4 or later to be installed on the streaming server.
Ogg Vorbis playback is supported in Mozilla Firefox, Google Chrome and Opera browsers, via jPlayer (http://jplayer.org/), and is also supported in several popular media players, including VideoLAN Client, also known as VLC (http://www.videolan.org/vlc/). (See the chapter Stream player for your website on how to deliver jPlayer to your audience). Ogg Opus is relatively new and is supported natively in the very latest browsers, such as Mozilla Firefox 25.0, and media players including VLC 2.0.4 or later.
Streaming MP3 below a bitrate of 128kbps is not recommended for music, because of a perceptible loss of high audio frequencies in the broadcast playout. A 96kbps or 64kbps MP3 stream may be acceptable for voice broadcasts if there is a requirement for compatibility with legacy hardware playback devices which do not support Ogg Vorbis or Opus streams.
Because LibreTime supports simultaneous streaming in multiple formats, it is possible to offer one or more streams via your website, and another independent stream for direct connection from hardware players. You can test whether Ogg streams sound better at low bitrates for yourself, by using the LISTEN button in LibreTime’s Master Panel to switch between streaming formats.
Conversely, you may have a music station which wants to stream at 160kbps or 192kbps to offer a quality advantage over stations streaming at 128kbps or less. Since Ogg, AAC and MP3 formats use lossy compression, listeners will only hear the benefit of higher streaming bitrates if the media files in the LibreTime storage server are encoded at an equivalent bitrate, or higher.
When sending metadata about your stream to an Icecast server in non-Latin alphabets, you may find that Icecast does not display the characters correctly for an MP3 stream, even though they are displayed correctly for an Ogg Vorbis stream. In the following screenshot, Russian characters are being displayed incorrectly in the Current Song field for the MP3 stream:
The solution is to specify that the metadata for the MP3 mount point you are using should be interpreted using UTF-8 encoding. You can do this by adding the following stanza to the /etc/icecast2/icecast.xml file, where libretime.mp3 is the name of your mount point:
<mount> <mount-name>/libretime.mp3</mount-name> <charset>UTF-8</charset> </mount>
After saving the /etc/icecast2/icecast.xml file, you should restart the Icecast server:
sudo invoke-rc.d icecast2 restart Restarting icecast2: Starting icecast2 Detaching from the console icecast2.
In a typical radio station configuration, the live output from the broadcast studio and the scheduled output from LibreTime are mixed together before being sent further along the broadcast chain, to a transmitter or streaming media server on the Internet. (This may not be the case if your LibreTime server is remote from the studio, and you are using the Show Source Mount Point or Master Source Mount Point to mix live and scheduled content. See the Stream Settings chapter for details).
If your Icecast server is hosted in a remote data centre, you may not have the option to handover the streaming media source manually, because you have no physical access to connect a broadcast mixer to the server. Disconnecting the stream and beginning another is less than ideal, because the audience’s media players will also be disconnected when that happens.
The Icecast server has a fallback-mount feature which can be used to move clients (media players used by listeners or viewers) from one source to another, as new sources become available. This makes it possible to handover from LibreTime output to a show from another source, and handover to LibreTime again once the other show has ended.
To enable fallback mounts, edit the main Icecast configuration file to define the mount points you will use, and the relationship between them.
sudo nano /etc/icecast2/icecast.xml
The example *
<mount> <mount-name>/airtime_128</mount-name> <hidden>0</hidden> </mount> <mount> <mount-name>/live.ogg</mount-name> <fallback-mount>/airtime_128</fallback-mount> <fallback-override>1</fallback-override> <hidden>0</hidden> </mount> <mount> <mount-name>/stream.ogg</mount-name> <fallback-mount>/live.ogg</fallback-mount> <fallback-override>1</fallback-override> <hidden>0</hidden> </mount>
These mount point definitions mean that a client connecting to a URL such as http://icecast.example.com:8000/stream.ogg will first fall back to the /live.ogg mount point if it is available. If not, the client will fall back in turn to the /airtime_128 mount point for LibreTime playout.
Setting the value of *
Connect the other source to the Icecast server with the same parameters defined in the /etc/airtime/liquidsoap.cfg file, except for the mount point. This should one of the mount points you have defined in the /etc/icecast2/icecast.xml file, such as /live.ogg in the example above.
To configure Mixxx for streaming to Icecast, click Options, Preferences, then Live Broadcasting. For server Type, select the default of Icecast 2 when streaming to Debian or Ubuntu servers, as this is the current version of Icecast supplied with those GNU/Linux distributions.
By default, Icecast streams are buffered to guard against network problems, which causes latency for remote listeners. When monitoring the stream from a remote location, you may have to begin the live stream a few seconds before the previous stream ends to enable a smooth transition.