auditok.util.make_channel_selector

auditok.util.make_channel_selector(sample_width, channels, selected=None)

Create and return a callable used for audio channel selection. The returned selector can be used as selector(audio_data) and returns data that contains selected channel only.

Importantly, if selected is None or equals “any”, selector(audio_data) will separate and return a list of available channels: [data_channe_1, data_channe_2, …].

Note also that returned selector expects bytes format for input data but does notnecessarily return a bytes object. In fact, in order to extract the desired channel (or compute the average channel if selected = “avg”), it first converts input data into a array.array (or numpy.ndarray) object. After channel of interst is selected/computed, it is returned as such, without any reconversion to bytes. This behavior is wanted for efficiency purposes because returned objects can be directly used as buffers of bytes. In any case, returned objects can be converted back to bytes using bytes(obj).

Exception to this is the special case where channels = 1 in which input data is returned without any processing.

Parameters:

• sample_width (int) – number of bytes used to encode one audio sample, should be 1, 2 or 4.
• channels (int) – number of channels of raw audio data that the returned selector should expect.
• selected (int or str, default: None) – audio channel to select and return when calling selector(raw_data). It should be an int >= -channels and < channels. If one of “mix”, “avg” or “average” is passed then selector will return the average channel of audio data. If None or “any”, return a list of all available channels at each call.

Returns:

selector – a callable that can be used as selector(audio_data) and returns data that contains channel of interst.

Return type:

callable

Raises:

ValueError – if sample_width is not one of 1, 2 or 4, or if selected has an unexpected value.