July 3, 2019

Passing Icecast metadata in Nimble Live Transcoder

Nimble Streamer has an advanced audio streaming feature set. Live audio streaming covers transmuxing of Icecast pulled and published streams, audio transcoding in Nimble Live Transcoder and ads insertion via Nimble Advertizer.

Metadata is an important part of Icecast usage. We've previously added appending Icecast metadata to live streams and Icecast metadata passthrough tags support. However, by default Live Transcoder doesn't pass metadata through when transforming audio content.

Our long-term customers StreamGuys, who extensively use our audio streaming features, asked if we might add a passthrough of Icecast metadata while using Live Transcoder. Our clients' feedback has always driven our development so we keep adding elements which are helpful to entire audio streamers community.

We're glad to announce that we've improved Live Transcoder to allow setting up metadata passthrough for audio. This feature needs some additional setup so follow the instructions below if you'd like to use it.

1. Set up Nimble configuration

First, this feature needs to be explicitly enabled for the server.

Add this parameter into your nimble.conf file:
icecast_forward_metadata_through_encoder_enabled = true
Then re-start Nimble Streamer instance. This reference page describes how you can work with Nimble configuration in general.

2. Adjusting transcoding scenario

You can use 2 different options to enable metadata forwarding, each having its specific use case.

We assume you're already familiar with Live Transcoder setup and you already know how to create a transcoding scenario where you need the metadata to pass. You can take a look at Transcoder website and a set of videos to refresh your knowledge.

2.a Add new parameter

To make the output stream to have a metadata from some incoming stream, you need to add icecast_metadata_source custom parameter to audio encoder settings.

As the encoder element of transcoder scenario allows receiving content and other data from any decoded stream, with additional filtering on top, you need to specify which stream is used as a source for your metadata.

Specifying exact name

Take a look at an example of encoder setting.

Here you see original content blue decoding element with application name "live" and stream name "origin". For encoder output element you see new app and stream names and also additional "icecast_metadata_source" parameter with "live/origin" value which indicates the exact original stream.

Specifying wildcard stream name

Live Transcoder allows using wildcard stream name for the convenience of setup. Take a look at this example.

Here you can see decoder element has "live" app name and "*" as a stream name. This means decoder has no stream name specified which allows using whatever incoming stream name you have. If you look at encoder settings, you can see "{STREAM}_output" as a stream name, where {STREAM} is a placeholder for any input stream. So in the example above if your input is "live/radio", your output will be "live_radio/radio_output".

This wildcard approach is also used for "icecast_metadata_source" parameter. In our example you see "live/{STREAM}" as a value. This means that if your input source is "live/radio", then "live/radio" will be used as a source of metadata.

You can also simplify the setup process further. If your decoder app name and encoder app name are the same, you can skip the app name in parameter value and keep only {STREAM} as shown below.

In this case the application name is "inherited" from the encoder application ("live" in this case) which is equal to source decoder app name.

This approach allows taking metadata from any input live stream available in Nimble Streamer.

2.b Forwarding of input metadata

You can forward whatever metadata is available in the processed stream. Just check the "Forward Icecast metadata" boxes in both decoder and encoder elements.


This approach allows using forwarding as part of failover and hotswap feature set. As a downside, this case doesn't "remember" the use metadata which was present before the switch to this scenario or stream.

3. Apply new setting

Metadata passthrough cannot be applied on-the-fly to a transcoding scenario unlike other parameters. In order to make it work you need to save your scenario and then perform either of these steps:

  • Re-start the input stream
  • Or pause/resume the scenario. Go to scenarios list, click Pause icon, wait for the pause to sync with the transcoder, click on resume icon to start it again.

Once you do any of those 2 options, the metadata will become available in your output.

RTMP Icecast metadata

RTMP protocol is able to carry Icecast metadata and Nimble Streamer can put such RTMP metadata into Icecast streams. However, if you'd like to pass that metadata through Live Transcoder, you need to follow these instructions for proper setup.

Let us know if you have any suggestions or questions about our Icecast feature set, we're opened for discussions.

Related documentation

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