How to make ffmpeg write 16 bit ALAC?

Question

MacOS Sierra, ffmpeg version 3.0.2.

Trying to change the volume of a file in ALAC encoding (Apple Lossless 16 bit):

ffmpeg -i input.m4a -af "volume=0.5" -acodec alac output.m4a

I was following the advice given in the Wiki https://trac.ffmpeg.org/wiki/How%20to%20change%20audio%20volume%20up-down%20with%20FFmpeg, and I have specified "-acodec alac", because the extension "m4a" is - by default - related to AAC, rather than ALAC.

Problem: ffmpeg would write a 24 bit ALAC file, rather than the usual 16 bit ALAC.

Question: How can I make ffmpeg write 16 bit ALAC?

Answer 1

Use

ffmpeg -i input.m4a -af "volume=0.5" -acodec alac -sample_fmt s16p output.m4a