How to tell ffmpeg to copy all streams except one audio stream (to encode)?

Question

Input:

 * One Video
 * 4 audio streams
 * Many subtitles
 * Chapters

I want to re-encode one of the audio streams (the first one) and keep everything else as-of (copy).
Is it possible to do that in one command-line in ffmpeg?

So far my best 2 guesses don't work:

ffmpeg -i input.mkv -map_metadata 0 -map 0:v -c:v copy -map 0:s -c:s copy -map 0:a:0 -c:a ac3 -vbr 3 -map 0:a:1 -c:a copy -map 0:a:2 -c:a copy -map 0:a:3 -c:a copy output.mkv
Copies everything

ffmpeg -i input.mkv -map_metadata 0 -map 0:v -c:v copy -map 0:s -c:s copy -map 0:a -c:a copy -map 0:a:0 -c:a ac3 -vbr 3 output.mkv
Re-encodes all audio streams

Answer 1

Use

ffmpeg -i input.mkv -map_metadata 0 -map 0 -c copy -c:a:0 ac3 -vbr 3 output.mkv

See https://superuser.com/a/1219824 for an illustrated guide to how stream options are parsed.