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• modprobe snd-dummy on linux server, ffmpeg -f alsa is recording noise

  20 mars 2021, par booksword

  Some people say that the parameter fake_buffer can remove the noise, but I tried it and there is still noise

  


  


  modprobe snd-dummy fake_buffer=0

  


  


  #modprobe snd-dummy fake_buffer=0 
# lsmod |grep snd
snd_dummy              24576  0
snd_pcm_oss            61440  0
snd_mixer_oss          28672  1 snd_pcm_oss
snd_pcm               118784  2 snd_pcm_oss,snd_dummy
snd_timer              36864  1 snd_pcm
snd                    94208  5 snd_timer,snd_pcm_oss,snd_pcm,snd_dummy,snd_mixer_oss
soundcore              16384  1 snd
# modinfo snd_dummy
filename:       /lib/modules/4.14.129-bbrplus/kernel/sound/drivers/snd-dummy.ko
license:        GPL
description:    Dummy soundcard (/dev/null)
author:         Jaroslav Kysela <perex@perex.cz>
depends:        snd-pcm,snd
retpoline:      Y
intree:         Y
name:           snd_dummy
vermagic:       4.14.129-bbrplus SMP mod_unload modversions 
parm:           index:Index value for dummy soundcard. (array of int)
parm:           id:ID string for dummy soundcard. (array of charp)
parm:           enable:Enable this dummy soundcard. (array of bool)
parm:           model:Soundcard model. (array of charp)
parm:           pcm_devs:PCM devices # (0-4) for dummy driver. (array of int)
parm:           pcm_substreams:PCM substreams # (1-128) for dummy driver. (array of int)
parm:           fake_buffer:Fake buffer allocations. (bool)
parm:           hrtimer:Use hrtimer as the timer source. (bool)

#aplay -L
null
    Discard all samples (playback) or generate zero samples (capture)
pulse
    PulseAudio Sound Server
dummy
default:CARD=Dummy
    Dummy, Dummy PCM
    Default Audio Device
sysdefault:CARD=Dummy
    Dummy, Dummy PCM
    Default Audio Device
dmix:CARD=Dummy,DEV=0
    Dummy, Dummy PCM
    Direct sample mixing device
dsnoop:CARD=Dummy,DEV=0
    Dummy, Dummy PCM
    Direct sample snooping device
hw:CARD=Dummy,DEV=0
    Dummy, Dummy PCM
    Direct hardware device without any conversions
plughw:CARD=Dummy,DEV=0
    Dummy, Dummy PCM
    Hardware device with all software conversions


# ffmpeg -f alsa  -i hw:0 -t 5  /dev/shm/out.mp3 -y
ffmpeg version 3.4.8-0ubuntu0.2 Copyright (c) 2000-2020 the FFmpeg developers
  built with gcc 7 (Ubuntu 7.5.0-3ubuntu1~18.04)
  configuration: --prefix=/usr --extra-version=0ubuntu0.2 --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --enable-gpl --disable-stripping --enable-avresample --enable-avisynth --enable-gnutls --enable-ladspa --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcdio --enable-libflite --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm --enable-libmp3lame --enable-libmysofa --enable-libopenjpeg --enable-libopenmpt --enable-libopus --enable-libpulse --enable-librubberband --enable-librsvg --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libtwolame --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx265 --enable-libxml2 --enable-libxvid --enable-libzmq --enable-libzvbi --enable-omx --enable-openal --enable-opengl --enable-sdl2 --enable-libdc1394 --enable-libdrm --enable-libiec61883 --enable-chromaprint --enable-frei0r --enable-libopencv --enable-libx264 --enable-shared
  libavutil      55. 78.100 / 55. 78.100
  libavcodec     57.107.100 / 57.107.100
  libavformat    57. 83.100 / 57. 83.100
  libavdevice    57. 10.100 / 57. 10.100
  libavfilter     6.107.100 /  6.107.100
  libavresample   3.  7.  0 /  3.  7.  0
  libswscale      4.  8.100 /  4.  8.100
  libswresample   2.  9.100 /  2.  9.100
  libpostproc    54.  7.100 / 54.  7.100
Guessed Channel Layout for Input Stream #0.0 : stereo
Input #0, alsa, from 'hw:0':
  Duration: N/A, start: 1616225206.353453, bitrate: 1536 kb/s
    Stream #0:0: Audio: pcm_s16le, 48000 Hz, stereo, s16, 1536 kb/s
Stream mapping:
  Stream #0:0 -> #0:0 (pcm_s16le (native) -> mp3 (libmp3lame))
Press [q] to stop, [?] for help
Output #0, mp3, to '/dev/shm/out.mp3':
  Metadata:
    TSSE            : Lavf57.83.100
    Stream #0:0: Audio: mp3 (libmp3lame), 48000 Hz, stereo, s16p
    Metadata:
      encoder         : Lavc57.107.100 libmp3lame
size=      79kB time=00:00:05.01 bitrate= 129.0kbits/s speed=   1x     
video:0kB audio:79kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.293899%




  


  i use alsamixer to set all Volume to 0 ,and there is still noise
I searched in google for a long time and did not find other people have this problem , where am I doing it wrong

  


• ffmpeg : Continuous streaming plus recording at random time

  21 juin 2014, par Ralf Anderson

  It’s possible to stream and record the same input at the same time with ffmpeg. What I want to do though, is only start (and stop) recording at some random point later.

  Is it possible to somehow tell the active ffmpeg process (which is already streaming) to also start recording ?
  My first alternative was to simply start another ffmpeg process just to record, but the source input will be blocked by the first ffmpeg process streaming it and the stream will be blocked by the viewer displaying the stream on screen, so I can’t access anything to record. Can I change something so the stream/source input is not reserved for just one receiver ?

  In my concrete scenario, the source input is a webcam, which I want to continuously display plus be able to record at user-driven time. I stream the webcam using ffmpeg via udp to the localhost and can view it with a suitable player. I just can’t record it while also viewing and vice versa.

  I also tried the "Tee Muxer", which can generate multiple outputs with the same ffmpeg instance. I streamed it to the localhost on different ports, one to view and one to record.

  ffmpeg.exe -f dshow -i video="ManyCam Virtual Webcam" -map 0 -vcodec h264 -r 25 -f tee "[f=mpegts]udp://127.0.0.1:33333/|[f=mpegts]udp://127.0.0.1:33334/"

  This works fine, except for the delay of about 500ms, which I only get when I stream, not when I access the Webcam directly with ffplay e.g.. I was expecting no delay at all, since it’s all local, but I suppose this comes from the encoding ? I’ve tried streaming the raw video (setting -vcodec rawvideo), but I can neither view it with ffplay nor record it. Are there some special parameters needed for rawvideo ? After all, the input for the stream is rawvideo too, according to ffmpeg.

  I have not yet looked at ffserver, but I assume it would be no different to generating multiple outputs with tee muxer in my use case ?

  If I somehow could be able to display/record the stream generated by

  ffmpeg.exe -f dshow -i video="ManyCam Virtual Webcam" -map 0 -vcodec rawvideo -r 25 -f tee "[f=mpegts]udp://127.0.0.1:33333/|[f=mpegts]udp://127.0.0.1:33334/"

  then that would already suffice. Or changing the encoding in such a way that no compression is done at all should work just as well (if that’s causing the delay).

• Anomalie #3475 : Une mini coquille dans une clé de chaîne de langue du core

  12 juin 2015

  oui j’en ai parlé sur IRC ... j’ai commité puis envoyé un email à Kent1 pour correction.