FFmpeg `-map` Explained: Precisely Select Video, Audio, and Subtitle Streams

Thu, 02 Apr 2026 23:14:03 +0800

In multi-audio and multi-subtitle workflows, -map is one of FFmpeg’s most important and most frequently misused options.

If you don’t explicitly specify -map, FFmpeg auto-selects streams using default rules, and the output is often not what you expect. For example:

Subtitles disappear after export
The wrong language track is selected
Unwanted data streams are included

This article uses common real-world scenarios to explain how -map works.

First, Understand What a “Stream” Is

A container file (such as mp4 or mkv) usually contains multiple streams, including:

Video streams (v)
Audio streams (a)
Subtitle streams (s)
Attachment/data streams (fonts, cover art, chapters, etc.)

You can inspect streams with ffprobe:

`1`	`ffprobe -hide_banner input.mkv`

Basic `-map` Syntax

Most common pattern:

`1`	`-map input_index[:stream_type][:stream_index]`

Examples:

0:v: all video streams from the 1st input
0:a:0: the 1st audio stream from the 1st input
1:s:1: the 2nd subtitle stream from the 2nd input

Notes:

input_index starts from 0, based on -i order
stream_index also starts from 0

Practical Examples

1) Video from A, audio from B

ffmpeg -i english.mp4 -i french.mp3 \
  -map 0:v:0 -map 1:a:0 \
  -c:v copy -c:a aac \
  french.mp4

Meaning:

Use the first video stream from english.mp4
Use the first audio stream from french.mp3
Merge into french.mp4

2) Keep all streams from input 1, then add one more audio track

ffmpeg -i english.mp4 -i french.mp3 \
  -map 0 -map 1:a:0 \
  -c copy \
  english-french.mp4

Meaning:

-map 0 keeps all streams from the first input
Then append the first audio stream from the second input

Two Useful Advanced Tricks

1) Negative mapping: exclude unwanted streams

For example, keep everything from input 1 but remove its second audio stream:

`1`	`ffmpeg -i input.mkv -map 0 -map -0:a:1 -c copy output.mkv`

2) Optional mapping: don’t fail when a stream is missing

If some files may not have subtitles, use ?:

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

0:s? means: map subtitles if present; otherwise skip without error.

Common Pitfalls

Once you use -map, FFmpeg stops automatic stream selection, so you must map everything you need.
-c copy only remuxes without transcoding. If the target container doesn’t support a codec, it still fails.
With multiple inputs, index mistakes are common. Input indices are determined only by -i order.
For robust scripts, inspect with ffprobe first, then generate -map dynamically.

Summary

The core idea of -map is simple: explicitly tell FFmpeg which input to use, what stream type to pick, and which stream index to select.

Once you master this, you can reliably handle complex cases like multi-audio, multi-subtitle, and cross-file stream composition.

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