&proaudiocurrently do the same thing, so they are just aliases of each other. When used, they can be used to setup the audio transfer pipeline to allow for unprocessed, high-bitrate, stereo audio.
&stereoflag add to their URL.
&mono. These flags will override the presets applied by the
&stereoflag. Please note, depending on your browser, enabling
&dncan force disable stereo audio.
stereo=1, which if enabled: