Measures phase of input audio, which is exported as metadata lavfi.aphasemeter.phase,
representing mean phase of current audio frame. A video output can also be produced and is
enabled by default. The audio is passed through as first output.
Audio will be rematrixed to stereo if it has a different channel layout. Phase value is in
range [-1, 1] where -1 means left and right channels are completely out of phase
and 1 means channels are in phase.
The filter accepts the following options, all related to its video output:
- rate, r
-
Set the output frame rate. Default value is
25. - size, s
-
Set the video size for the output. For the syntax of this option, check the "Video size" section in the ffmpeg-utils manual. Default value is
800x400. - rc, gc, bc
-
Specify the red, green, blue contrast. Default values are
2,7and1. Allowed range is[0, 255]. - mpc
-
Set color which will be used for drawing median phase. If color is
nonewhich is default, no median phase value will be drawn. - video
-
Enable video output. Default is enabled.
phasing detection
The filter also detects out of phase and mono sequences in stereo streams. It logs the sequence start, end and duration when it lasts longer or as long as the minimum set.
The filter accepts the following options for this detection:
- phasing
-
Enable mono and out of phase detection. Default is disabled.
- tolerance, t
-
Set phase tolerance for mono detection, in amplitude ratio. Default is
0. Allowed range is[0, 1]. - angle, a
-
Set angle threshold for out of phase detection, in degree. Default is
170. Allowed range is[90, 180]. - duration, d
-
Set mono or out of phase duration until notification, expressed in seconds. Default is
2.
Examples
-
Complete example with ffmpeg to detect 1 second of mono with 0.001 phase tolerance:
ffmpeg -i stereo.wav -af aphasemeter=video=0:phasing=1:duration=1:tolerance=0.001 -f null -