Comment by smalltorch

So this is only for termux compatibility. On a standard distro it skips this step entirely and goes straight from raw pcm to opus.

On termux 'termux-microphone-record' is a wrapper around androids 'mediarecorder'. It doesn't support raw pcm output. It records AAC in m4a wrapper and then the extra ffmpeg package converts this to rawpcm so it can follow the same pipeline.