[FFmpeg-user] delay time in live ultrasound converter

[Michael Koch]

Hello,

I'm using the following batch file (Windows 7) for a live ultrasound 
conversion.

set "SR=44100"             :: Sample rate
set "F=14000"              :: Subtracted frequency
set "VOL=10"               :: Volume factor
set /a "N=4096*%F%/%SR%"   :: N = 4096 * F / SR

c:\ffmpeg\ffmpeg -f dshow -sample_rate %SR% -sample_size 16 -channels 2 
-i audio="Microphone (SoundMAX Integrated" -af 
volume=%VOL%,afftfilt='real=if(lt(b+%N%,nb),real(b+%N%,ch),0)':'imag=if(lt(b+%N%,nb),imag(b+%N%,ch),0)' 
-f nut - | c:\ffmpeg\ffplay -

FFmpeg gets the audio input from the computer's microphone input and 
passes the converted output to FFplay.
This works fine for hearing bats, but it has about 1-2 seconds delay 
between input and output.
Are there any options for minimizing the delay?

The console output is copied below.

Thanks,
Michael


C:\Users\mkoch\Desktop\Ultrasound Live>c:\ffmpeg\ffmpeg -f dshow 
-sample_rate 44
100 -sample_size 16 -channels 2 -i audio="Microphone (SoundMAX 
Integrated" -af v
olume=10,afftfilt='real=if(lt(b+1300,nb),real(b+1300,ch),0)':'imag=if(lt(b+1300,
nb),imag(b+1300,ch),0)' -f nut -   | c:\ffmpeg\ffplay -
ffmpeg version N-92857-g3e461f9d4c Copyright (c) 2000-2018 the FFmpeg 
developers

   built with gcc 8.2.1 (GCC) 20181201
   configuration: --enable-gpl --enable-version3 --enable-sdl2 
--enable-fontconfi
g --enable-gnutls --enable-iconv --enable-libass --enable-libbluray 
--enable-lib
freetype --enable-libmp3lame --enable-libopencore-amrnb 
--enable-libopencore-amr
wb --enable-libopenjpeg --enable-libopus --enable-libshine 
--enable-libsnappy --
enable-libsoxr --enable-libtheora --enable-libtwolame --enable-libvpx 
--enable-l
ibwavpack --enable-libwebp --enable-libx264 --enable-libx265 
--enable-libxml2 --
enable-libzimg --enable-lzma --enable-zlib --enable-gmp 
--enable-libvidstab --en
able-libvorbis --enable-libvo-amrwbenc --enable-libmysofa 
--enable-libspeex --en
able-libxvid --enable-libaom --enable-libmfx --enable-amf 
--enable-ffnvcodec --e
nable-cuvid --enable-d3d11va --enable-nvenc --enable-nvdec 
--enable-dxva2 --enab
le-avisynth --enable-libopenmpt
   libavutil      56. 25.100 / 56. 25.100
   libavcodec     58. 42.104 / 58. 42.104
   libavformat    58. 25.100 / 58. 25.100
ffplay version N-92857-g3e461f9d4c  libavdevice    58.  6.101 / 58. 
6.101 Copyr
ight (c) 2003-2018 the FFmpeg developers

   libavfilter     7. 46.101 /  7. 46.101  built with gcc 8.2.1 (GCC) 
20181201

   configuration: --enable-gpl --enable-version3 --enable-sdl2 
--enable-fontconfi
g --enable-gnutls --enable-iconv --enable-libass --enable-libbluray 
--enable-lib
freetype --enable-libmp3lame --enable-libopencore-amrnb 
--enable-libopencore-amr
wb --enable-libopenjpeg --enable-libopus --enable-libshine 
--enable-libsnappy --
enable-libsoxr --enable-libtheora --enable-libtwolame --enable-libvpx 
--enable-l
ibwavpack --enable-libwebp --enable-libx264 --enable-libx265 
--enable-libxml2 --
enable-libzimg --enable-lzma --enable-zlib --enable-gmp 
--enable-libvidstab --en
able-libvorbis --enable-libvo-amrwbenc --enable-libmysofa 
--enable-libspeex --en
able-libxvid --enable-libaom --enable-libmfx --enable-amf 
--enable-ffnvcodec --e
nable-cuvid --enable-d3d11va --enable-nvenc --enable-nvdec 
--enable-dxva2 --enab
le-avisynth --enable-libopenmpt
   libswscale      5.  4.100 /  5.  4.100
   libswresample   3.  4.100 /  3.  4.100
   libpostproc    55.  4.100 / 55.  4.100
   libavutil      56. 25.100 / 56. 25.100
   libavcodec     58. 42.104 / 58. 42.104
   libavformat    58. 25.100 / 58. 25.100
   libavdevice    58.  6.101 / 58.  6.101
   libavfilter     7. 46.101 /  7. 46.101
   libswscale      5.  4.100 /  5.  4.100
   libswresample   3.  4.100 /  3.  4.100
   libpostproc    55.  4.100 / 55.  4.100
Guessed Channel Layout for Input Stream #0.0 : stereo    0B f=0/0
Input #0, dshow, from 'audio=Microphone (SoundMAX Integrated':
   Duration: N/A, start: 1701.243000, bitrate: 1411 kb/s
     Stream #0:0: Audio: pcm_s16le, 44100 Hz, stereo, s16, 1411 kb/s
Stream mapping:
   Stream #0:0 -> #0:0 (pcm_s16le (native) -> vorbis (libvorbis))
Press [q] to stop, [?] for help
Output #0, nut, to 'pipe:': aq=    0KB vq=    0KB sq=    0B f=0/0
   Metadata:
     encoder         : Lavf58.25.100
     Stream #0:0: Audio: vorbis (libvorbis) (oV[0][0] / 0x566F), 44100 
Hz, stereo
, fltp
     Metadata:
       encoder         : Lavc58.42.104 libvorbis
Input #0, nut, from 'pipe:':
   Metadata:
     encoder         : Lavf58.25.100
   Duration: N/A, start: 0.000000, bitrate: N/A
     Stream #0:0: Audio: vorbis (oV[0][0] / 0x566F), 44100 Hz, stereo, fltp
     Metadata:
       encoder         : Lavc58.42.104 libvorbis
   16.27 M-A:  0.000 fd=   0 aq=    3KB vq=    0KB sq=    0B f=0/0