July 7, 2016

Manipulating audio channels in Nimble Streamer Live Transcoder

Live Transcoder for Nimble Streamer has rich audio transformation feature set which is based on audio filters and AAC decoding/encoding. Besides common operations like volume control, changing sample rate or bitrate, you can set up any FFmpeg filters.

Let's see an interesting task for channels manipulation which can be accomplished with Nimble Streamer Live Transcoder.

Different language channels

There's a stream with video and stereo audio where each of the audio channels has its own language. The goal is to create 2 streams with identical video and different audio, each stream having its language.

We assume you've already installed Transcoder. If not, use this procedure. You can check our videos describing general setup process to get familiar with the UI. As a result you need to set up transcoding scenario as shown below.

As you can see, first we've made 2 passthrough videos.

The next step is to split audio after it's decoded to avoid any resources usage overhead.
Then you can see the key element which is "Pan" filter which goes all the magic. It's applied to each of the split audio streams. You can read FFmpeg audio manipulation page for more details about pan filter usage.

Check to pictures below to see each of the filters' settings. Those are:

  • stereo|c0=c0|c1=c0
  • stereo|c0=c1|c1=c1

All you need after that is to add 2 standard AAC audio encoders.

Stereo to mono

As in previous case, you need to use "pan" filter to create mono stream from stereo.
Filter setting is as follows:
It looks like this:

Mono to stereo

This can be done with the following "pan" filter settings:
Filter dialog will look like this:

This type of setting can be used in scenarios like multi-language ABR.

5.1 to stereo

If you have 5.1 (side) to stereo use case, you need to add Pan filter with this parameter:
Here one channel will take Front Center + Front Left + Side Left and another one will take Front Center + Front Right + Side Right.

For 5.1 to stereo use case you can use this parameter:
This will have one channel take Front Center + Front Left + Back Left and another one will take Front Center + Front Right + Back Right.

You can check audio layouts names on this page.

That's it. When the scenario is saved, it's applied to the Transcoder instance. The result stream will be delivered via any protocol which you defined for corresponding applications, e.g. RTMP, HLS etc.

To set up more audio encoding parameters, please check Audio encoder parameters video on our YouTube channel. Specifically, read more about re-sampling audio.

Feel free to visit Live Transcoder webpage for other details and contact us if you have any question.

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