Null audio source, never return audio frames. It is mainly useful as a template and to be employed in analysis / debugging tools.

It accepts as optional parameter a string of the form sample_rate:channel_layout.

sample_rate specify the sample rate, and defaults to 44100.

channel_layout specify the channel layout, and can be either an integer or a string representing a channel layout. The default value of channel_layout is 3, which corresponds to CH_LAYOUT_STEREO.

Check the channel_layout_map definition in libavcodec/audioconvert.c for the mapping between strings and channel layout values.

Follow some examples:

#  set the sample rate to 48000 Hz and the channel layout to CH_LAYOUT_MONO.
anullsrc=48000:4

# same as
anullsrc=48000:mono