ffmpeg stereo channels into two mono channels

I wanted to know if there is a way to split stereo into two mono wav files. My first guess was

ffmpeg -threads "16" -i "$2" -map 0:1:1 "$3"

because my example video has the following informations:

Audio
ID                                       : 2
Format                                   : AAC
Format/Info                              : Advanced Audio Codec
Format profile                           : LC
Codec ID                                 : 40
Duration                                 : 39mn 0s
Bit rate mode                            : Constant
Bit rate                                 : 256 Kbps
Channel(s)                               : 2 channels
Channel positions                        : Front: L R

So I have this one audio stream with two channels and want two mono channels. At first I tried it with map_channel, but that didn't do the trick instead I was getting an error message:

Syntax error, mapchan usage: [file.stream.channel|-1][:syncfile:syncstream]

So I have tried it again with the above mentioned code and at least ffmpeg did something, but the outcome was not what I expected, instead of breaking it down into two mono wav files, the outcome was:

info.system.container = WAVE
info.system.size = 449413166 Bytes
info.system.size = 428.59 MiB
info.system.playtime = 2340.69 s
info.audio0.codec = PCM
info.audio0.desc = 
info.audio0.format_endianness = Little
info.audio0.format_sign = Signed
info.audio0.format_resolution = 16 bits
info.audio0.samprate = 48000 Hz
info.audio0.channels = 2

again with two audio channels, so where did I go wrong?

Using ffmpeg there are several methods that I know of to go from stereo to two individual mono files, or two mono streams in one file:

stereo to 2 mono outputs

-map_channel option

ffmpeg -i stereo.wav -map_channel 0.0.0 left.wav -map_channel 0.0.1 right.wav

pan audio filter

ffmpeg -i stereo.wav -filter_complex \
"[0:0]pan=1|c0=c0[left]; \
 [0:0]pan=1|c0=c1[right]" \
-map "[left]" left.wav -map "[right]" right.wav

stereo to 2 mono streams

channelsplit audio filter

This will create one output file that has two individual mono streams:

ffmpeg -i input.m4a -filter_complex channelsplit out.mka

Also see

• Manipulating audio channels with ffmpeg

You should use channelsplit filter for that. -map can not do this. For example:

ffmpeg -i in.mp3 -filter_complex channelsplit out.mkv

Check link to documentation that I've provided.