ffmpeg - mapping an audio file with 2 channels to a video file?
Channels are conjoint tracks within a single stream, so a stereo audio WAV has one stream which contains two channels. If this is what you have, use

ffmpeg -i video -i audio -map 0:v -map 1:a output


If they are distinct streams, then the above command will still map all the streams, but for explicit specification, use

ffmpeg -i video -i audio -map 0:v -map 1:a:0 -map 1:a:1 output