Am 16.09.2018 um 22:25 schrieb Paul B Mahol:
On 9/16/18, Michael Koch <[email protected]> wrote:
Filter inputs will be auto-converted from any non-float formats to
float or double one. Float/double formats are in [-1 .. +1] interval.
Thank you very much for the amultiply filter, it works great!
Here is an example for an ultrasonic converter which downconverts the
15kHz - 25kHz band to the 0 - 10kHz band.
First make an input file for testing. This is a 2 second 19kHz tone
followed by 2 seconds silence:
c://ffmpeg/ffmpeg -f lavfi -i
"sine=frequency=19000:sample_rate=48000:duration=2" -af apad -t 4
ultrasonic.wav
Then use the downconverter:
c://ffmpeg/ffmpeg -i ultrasonic.wav -f lavfi -i
"sine=frequency=15000:sample_rate=48000" -filter_complex
"[0]highpass=f=15000,highpass=f=15000,highpass=f=15000,highpass=f=15000[sound];[1]volume=8[sine];[sound][sine]amultiply[mixed];[mixed]lowpass=f=10000,lowpass=f=10000,lowpass=f=10000,lowpass=f=10000"
out.wav
Nice, it might be better to use aevalsrc, because it have multichannel output.
you are right, in my example the 15kHz sine source was only mono, and so
the conversion did only work for one channel. I did change
[1]volume=8[sine]
to
[1]volume=8,aeval=val(0)|val(0)[sine]
and now it works for both channels.
Michael
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