This element performs audio mixing for live streams.

Live Audio Mixer starts to mix audio after the first input pad is added or, if latency option is set to nil, when start_mixing notification is send. From this point, the mixer will produce an audio until :schedule_eos notification and :end_of_stream are received on all input pads.

Mixer mixes only raw audio (PCM), so some parser may be needed to precede it in pipeline.

notifications

Notifications

• :schedule_eos - mixer will send end_of_stream when it processes all input streams. After sending :schedule_eos mixer will raise if it gets a new input pad.

• {:start_mixing, latency} - mixer will start mixing audio after latency (non_neg_integer()). Audio that will come before the notification will be buffered.

Input pads can have offset - it tells how much timestamps differ from mixer time.

element-options

Element options

Passed via struct Membrane.LiveAudioMixer.t/0

• prevent_clipping

  boolean()

  Default value: false
  Defines how the mixer should act in the case when an overflow happens.

  • If true, the wave will be scaled down, so a peak will become the maximal value of the sample in the format. See Membrane.AudioMixer.ClipPreventingAdder.
  • If false, overflow will be clipped to the maximal value of the sample in the format. See Membrane.AudioMixer.Adder.

• native_mixer

  boolean()

  Default value: false
  The value determines if mixer should use NIFs for mixing audio. Only clip preventing version of native mixer is available. See Membrane.AudioMixer.NativeAdder.

• latency

  non_neg_integer() | nil

  Default value: 200 |> Membrane.Time.milliseconds()
  The value determines after what time the clock will start interval that mixes audio in real time. Latency is crucial to quality of output audio, the smaller the value, the more packets will be lost. But the bigger the value, the bigger the latency of stream.

  Audio Mixer allows starting mixing earlier with parent_notification :start_mixing. In this case, stream_format has to be passed through options.

  If notification :start_mixing is sent after mixing has started, the message will be discarded

  Start mixing manually:

  • set latency to nil
  • mixing has to be started manually by sending:start_mixing notification.

• stream_format

  RawAudio.t() | nil

  Default value: nil
  The value defines a raw audio format of pads connected to the element. It should be the same for all the pads. It is necessary if latency is set to nil.

pads

Pads

input

:input

Accepted formats:

%RawAudio{sample_format: sample_format}
when sample_format in [:s8, :s16le, :s16be, :s24le, :s24be, :s32le, :s32be]

Pad options:

• offset

  Time.non_neg()

  Default value: 0
  Offset of the input audio at the pad.

output

:output

Accepted formats:

RawAudio