map 1:3 refers to "second input:fourth stream". This is an absolute method of mapping and will choose a specific stream regardless of type. The top command does not use any stream specifiers.The commands do the same thing, but use different syntax to map streams: The commands in the diagram above will select the video from input0.mp4 and the 3rd audio stream from input1.mkv to output.mp4. The -map option can also be used to exclude specific streams with negative mapping. The -map option is used to choose which streams from the input(s) should be included in the output(s).