How to Map Only the Second Audio Track in FFmpeg

This article provides a straightforward guide on how to use FFmpeg to select and extract only the second audio track from a media file. You will learn the exact command-line syntax, understand how FFmpeg indexes audio streams, and see practical examples of saving the second audio track as a standalone audio file or multiplexing it with the original video while discarding other audio tracks.

In FFmpeg, stream selection is handled using the -map option. FFmpeg indexes inputs and streams starting from zero. Therefore:

  • 0 represents the first input file.
  • a represents audio streams.
  • 1 represents the second stream of that type (since indexing starts at 0 for the first stream).

Using this indexing system, the second audio track of the first input file is represented as 0:a:1.

Extract Only the Second Audio Track to a New Audio File

To extract only the second audio track and save it as an independent audio file (e.g., MP3, AAC, or WAV) without re-encoding, use the following command:

ffmpeg -i input.mp4 -map 0:a:1 -c:a copy output.mp3

Command breakdown:

  • -i input.mp4: Specifies the input video or audio file.
  • -map 0:a:1: Instructs FFmpeg to only select the second audio track from the first input file.
  • -c:a copy: Copies the audio stream directly without re-encoding, preserving the original quality and processing the file instantly.
  • output.mp3: The name of the output audio file.

Keep the Video and Map Only the Second Audio Track

If you want to output a video file that contains the original video track but only the second audio track (discarding the first audio track), use this command:

ffmpeg -i input.mp4 -map 0:v:0 -map 0:a:1 -c copy output.mp4

Command breakdown:

  • -map 0:v:0: Selects the first video stream of the input file.
  • -map 0:a:1: Selects only the second audio stream.
  • -c copy: Copies both the video and audio streams directly without re-encoding.