Mix a single stereo stream down to a mono stream. Both channels of the stereo stream will be downmixed into the stream:
ffmpeg -i stereo.flac -ac 1 mono.flac
Note: Any out of phase stereo will cancel out.
Output each channel in stereo input to individual mono files:
ffmpeg -i stereo.wav -map_channel 0.0.0 left.wav -map_channel 0.0.1 right.wav
or with the pan audio filer:
ffmpeg -i stereo.wav -filter_complex "[0:0]pan=1c|c0=c0[left];[0:0]pan=1c|c0=c1[right]" -map "[left]" left.wav -map "[right]" right.wav
Output each channel in stereo input to individual mono streams in one output file with the channelsplit audio filter:
ffmpeg -i in.mp3 -filter_complex channelsplit=channel_layout=stereo out.mka
Note: Your player will likely play the first stream by default unless your player allows you to select the desired stream.
Create a stereo output from one mono input:
ffmpeg -i input.mp3 -ac 2 output.m4a
or with the amerge audio filter:
ffmpeg -i input.mp3 -filter_complex "[0:a][0:a]amerge=inputs=2[aout]" -map "[aout]" output.m4a
Note: These examples will not magically create a "true" stereo output from the mono input, but simply place the same audio into both the left and right channels of the output (both channels will be identical).
Create a stereo output from two mono inputs with the amerge audio filter:
ffmpeg -i left.mp3 -i right.mp3 -filter_complex "[0:a][1:a]amerge=inputs=2[aout]" -map "[aout]" output.mka
Combine 6 mono inputs into one 5.1 (6 channel) output with the amerge audio filter:
ffmpeg -i front_left.wav -i front_right.wav -i front_center.wav -i lfe.wav -i back_left.wav -i back_right.wav \
-filter_complex "[0:a][1:a][2:a][3:a][4:a][5:a]amerge=inputs=6[aout]" -map "[aout]" output.wav
All inputs must have the same sample rate and format. If inputs do not have the same duration the output will stop with the shortest.
Split a 5.1 channel input into individual per-channel files:
ffmpeg -i in.wav \
-filter_complex "channelsplit=channel_layout=5.1[FL][FR][FC][LFE][BL][BR]" \
-map "[FL]" front_left.wav \
-map "[FR]" front_right.wav \
-map "[FC]" front_center.wav \
-map "[LFE]" lfe.wav \
-map "[BL]" back_left.wav \
-map "[BR]" back_right.wav
To downmix you can simply use -ac 2:
ffmpeg -i 6channels.wav -ac 2 stereo.wav
Notes:
If you want to map specific channels and drop the rest you can use the pan audio filter. This will map the FL (Front Left) of the input to the FL of the output, and the FR (Front Right) of the input to the FR of the output:
ffmpeg -i 6channels.wav -af "pan=stereo|c0=FL|c1=FR" stereo.wav
You can also map specific channels by number. This example will map the first and third channels of the input to the first and second channels of the output.
ffmpeg -i 6channels.wav -af "pan=stereo|c0=c0|c1=c2" output.wav
If the = in a channel specification is replaced by <, then the gains for that specification will be renormalized so that the total is 1, thus avoiding clipping noise. See the pan audio filter documentation for additional information and examples.
Combine two stereo inputs into one stereo output with the amerge and pan audio filters:
ffmpeg -i input1.wav -i input2.wav -filter_complex "[0:a][1:a]amerge=inputs=2,pan=stereo|c0<c0+c2|c1<c1+c3[aout]" -map "[aout]" output.mp3
Or use -ac 2 instead of the pan audio filter:
ffmpeg -i input1.wav -i input2.wav -filter_complex "[0:a][1:a]amerge=inputs=2[aout]" -map "[aout]" -ac 2 output.mp3
Note: The output produced with the pan audio filter may not be identical to the output produced with -ac 2, so you'll have to listen to your outputs or view audio statistics to determine which output suits you.
A similar situation as above, but instead use the left and right channels from the first input to make the left channel out the output, and use the left and right channels of the second input to make the right channel of the output.
Just change the channel specifications in the pan filter:
ffmpeg -i input1.wav -i input2.wav -filter_complex "[0:a][1:a]amerge=inputs=2,pan=stereo|c0<c0+c1|c1<c2+c3[aout]" -map "[aout]" output.mp3
The pan audio filter has to be used in this situation instead of -ac 2 unlike the previous example.
The left and right channels of the output will each contain both the left and right channels of the input:
ffmpeg -i input.mp3 -af "pan=stereo|c0<c0+c1|c1<c0+c1" output.ogg
Switch left channel to right and right channel to left:
ffmpeg -i stereo.ogg -map_channel 0.0.1 -map_channel 0.0.0 output.wav
or with the pan audio filer:
ffmpeg -i stereo.ogg -af pan=stereo|c0=c1|c1=c0 output.wav
FFmpeg can produce virtual binaural acoustics files using sofalizer filter, most known channel layouts are supported for input, output is always stereo.
ffmpeg -i input.wav -af sofalizer=/path/to/sofa/file output.flac
SOFA files can be found on http://sofacoustics.org/data/database/ari/
This example will mute the first channel (the left channel) but keep the second channel as is:
ffmpeg -i stereo.wav -map_channel -1 -map_channel 0.0.1 output.wav
The astats audio filter can display information including length, DC offset, min/max levels, peak/RMS level dB:
$ ffmpeg -i input.wav -af astats -f null -
…
[Parsed_astats_0 @ 0x168a260] Channel: 1
[Parsed_astats_0 @ 0x168a260] DC offset: -0.001829
[Parsed_astats_0 @ 0x168a260] Min level: -0.605072
[Parsed_astats_0 @ 0x168a260] Max level: 0.607056
[Parsed_astats_0 @ 0x168a260] Peak level dB: -4.335430
[Parsed_astats_0 @ 0x168a260] RMS level dB: -20.298984
[Parsed_astats_0 @ 0x168a260] RMS peak dB: -12.303891
[Parsed_astats_0 @ 0x168a260] RMS trough dB: -35.352893
[Parsed_astats_0 @ 0x168a260] Crest factor: 6.283154
[Parsed_astats_0 @ 0x168a260] Flat factor: 0.000000
[Parsed_astats_0 @ 0x168a260] Peak count: 2
[Parsed_astats_0 @ 0x168a260] Channel: 2
[Parsed_astats_0 @ 0x168a260] DC offset: -0.001826
[Parsed_astats_0 @ 0x168a260] Min level: -0.585999
[Parsed_astats_0 @ 0x168a260] Max level: 0.608490
[Parsed_astats_0 @ 0x168a260] Peak level dB: -4.314931
[Parsed_astats_0 @ 0x168a260] RMS level dB: -20.519969
[Parsed_astats_0 @ 0x168a260] RMS peak dB: -12.056472
[Parsed_astats_0 @ 0x168a260] RMS trough dB: -36.784681
[Parsed_astats_0 @ 0x168a260] Crest factor: 6.460288
[Parsed_astats_0 @ 0x168a260] Flat factor: 0.000000
[Parsed_astats_0 @ 0x168a260] Peak count: 2
[Parsed_astats_0 @ 0x168a260] Overall
[Parsed_astats_0 @ 0x168a260] DC offset: -0.001829
[Parsed_astats_0 @ 0x168a260] Min level: -0.605072
[Parsed_astats_0 @ 0x168a260] Max level: 0.608490
[Parsed_astats_0 @ 0x168a260] Peak level dB: -4.314931
[Parsed_astats_0 @ 0x168a260] RMS level dB: -20.408071
[Parsed_astats_0 @ 0x168a260] RMS peak dB: -12.056472
[Parsed_astats_0 @ 0x168a260] RMS trough dB: -36.784681
[Parsed_astats_0 @ 0x168a260] Flat factor: 0.000000
[Parsed_astats_0 @ 0x168a260] Peak count: 2.000000
[Parsed_astats_0 @ 0x168a260] Number of samples: 1440706
Output from ffmpeg -layouts:
Individual channels:
NAME DESCRIPTION
FL front left
FR front right
FC front center
LFE low frequency
BL back left
BR back right
FLC front left-of-center
FRC front right-of-center
BC back center
SL side left
SR side right
TC top center
TFL top front left
TFC top front center
TFR top front right
TBL top back left
TBC top back center
TBR top back right
DL downmix left
DR downmix right
WL wide left
WR wide right
SDL surround direct left
SDR surround direct right
LFE2 low frequency 2
Standard channel layouts:
NAME DECOMPOSITION
mono FC
stereo FL+FR
2.1 FL+FR+LFE
3.0 FL+FR+FC
3.0(back) FL+FR+BC
4.0 FL+FR+FC+BC
quad FL+FR+BL+BR
quad(side) FL+FR+SL+SR
3.1 FL+FR+FC+LFE
5.0 FL+FR+FC+BL+BR
5.0(side) FL+FR+FC+SL+SR
4.1 FL+FR+FC+LFE+BC
5.1 FL+FR+FC+LFE+BL+BR
5.1(side) FL+FR+FC+LFE+SL+SR
6.0 FL+FR+FC+BC+SL+SR
6.0(front) FL+FR+FLC+FRC+SL+SR
hexagonal FL+FR+FC+BL+BR+BC
6.1 FL+FR+FC+LFE+BC+SL+SR
6.1(back) FL+FR+FC+LFE+BL+BR+BC
6.1(front) FL+FR+LFE+FLC+FRC+SL+SR
7.0 FL+FR+FC+BL+BR+SL+SR
7.0(front) FL+FR+FC+FLC+FRC+SL+SR
7.1 FL+FR+FC+LFE+BL+BR+SL+SR
7.1(wide) FL+FR+FC+LFE+BL+BR+FLC+FRC
7.1(wide-side) FL+FR+FC+LFE+FLC+FRC+SL+SR
octagonal FL+FR+FC+BL+BR+BC+SL+SR
hexadecagonal FL+FR+FC+BL+BR+BC+SL+SR+TFL+TFC+TFR+TBL+TBC+TBR+WL+WR
downmix DL+DR