ffmpeg音频合成命令全集
时间:2023-07-12 13:00:30.945 +0800 CST 浏览:5935

stereo → mono stream

stereomono.png

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.

stereo → 2 × mono files

stereo2monooutputs.png

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

stereo → 2 × mono streams

stereo2monostreams.png

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.

mono → stereo

monostereo.png

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).

2 × mono → stereo

2monostereo.png

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

6 × mono → 5.1

6mono5point1.png

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.

5.1 → 6 × mono

5point16mono.png

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

5.1 → stereo

5point1stereo.png

To downmix you can
simply use -ac 2:

ffmpeg -i 6channels.wav -ac 2 stereo.wav

Notes:

  • * By default when using -ac 2 the LFE channel is omitted. See “Digital Audio Compression Standard (Document A/52:2012)”, sections 6.1.12 and 7.8 for more downmixing info.
  • * ffmpeg integrates a default down-mix (and up-mix) system that should be preferred (the -ac option) over the pan filter unless you have very specific needs.

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.

2 × stereo → stereo

2stereostereo.png

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.

2stereostereob.png

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.

Mix both stereo channels to stereo

stereostereomix.png

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 stereo channels

mutestereochannel.png

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

Virtual Binaural Acoustics

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/


Mute a channel

mutestereochannel.png

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

Statistics

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

Layouts

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


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