Turning a 5.1 .mkv into 2.0 or 2.1
Solution 1:
ffmpeg -i input.mkv -map 0 -c copy -c:a aac -ac 2 output.mkv
-
-map 0map all streams instead of relying on the default stream selection which only includes 1 stream per type. -
-c copystream copy. -
-c:a aacuse the encoder named aac for all audio. -
-ac 2make all audio stereo.