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• ffmpeg : Apply a time-based expr to control intensity of lowpass, highpass, aphaser, or aecho [closed]

  17 mai 2024, par Wes Modes

  I am procedurally constructing complexFilters for ffmpeg via fluent-ffmpeg. My fluent-ffmpeg complex filters look like :

  


  {
   "filter": "volume",
   "options": {
       "volume": "min(1, max(0, ((cos(PI * t * 1 / 13) * 1 + cos(PI * t * 1 / 7) * 0.5 + cos(PI * t * 1 / 3) * 0.25) +
-0.5 ) * 0.75 * -1 + 0.5))",
       "eval": "frame"
    },
    "inputs": "track_1_output",
    "outputs": "track_1_adjusted"
},


  


  Note that I am using an expression to determine the volume dynamically.

  


  Here I'm testing on the command line, to understand the mysteries of lightly-documented ffmpeg filters. I'm fading in and out two sources, intertwined in the output. Now I want to apply lowpass, highpass, aphaser, and/or aecho to the transitions using a time-based expr.

  


  I've already succeeded using the volume filter to fade the sources in and out (Note that the sine has reversed polarity for the second volume filter) :

  


  # working fade in/out
ffmpeg -i knox.mp3 -i static.mp3 -filter_complex \
"[0:a] \
    volume = 'min(1, max(0, 0.5 + 0.5 * cos(PI * t / 5)))': eval=frame \
    [a0]; \
[1:a] \
    volume = 'min(1, max(0, 0.5 - 0.5 * cos(PI * t / 5)))': eval=frame \
    [a1]; \
[a0][a1]
    amix = inputs=2: duration=shortest" \
-c:a libmp3lame -q:a 2 output.mp3


  


  ffmpeg -filters says that lowpass has time-based support :

  


    T.. = Timeline support
 TSC lowpass           A->A       Apply a low-pass filter with 3dB point frequency.


  


  How can I similarly apply these other filters to source1 using a time-bassed expr ? I was unsuccessful in figuring out lowpass and highpass :

  


  # applying a lowpass filter
ffmpeg -i knox.mp3 -i static.mp3 -filter_complex \
"[0:a] \
    volume = 'min(1, max(0, 0.5 + 0.5 * cos(PI * t / 5)))': eval=frame, \
    lowpass=f=3000: mix='0.5 + 0.5 * cos(PI * t / 5)' \
    [a0]; \
[1:a] \
    volume = 'min(1, max(0, 0.5 - 0.5 * cos(PI * t / 5)))': eval=frame \
    [a1]; \
[a0][a1]
    amix = inputs=2: duration=shortest" \
-c:a libmp3lame -q:a 2 output.mp3


  


  With the resultant error :

  


  [Parsed_lowpass_1 @ 0x7f9a72005c00] [Eval @ 0x7ff7bec423d8] Undefined constant or missing '(' in 't/5)'
[Parsed_lowpass_1 @ 0x7f9a72005c00] Unable to parse option value "0.5 + 0.5 * cos(PI * t / 5)"
Error applying option 'mix' to filter 'lowpass': Invalid argument


  


  What complicated fffmpeg faerie magic is needed to make some of the filters other than volume controlled by a time-based expr ?

  


• How to change volume of an audio AVPacket

  28 mai 2023, par S B

  I have a desktop Qt-based application that fetches a sound stream from the network and plays it using QAudioOutput. I want to provide a volume control to the user so that he can reduce the volume. My code looks like this :

  



  float volume_control = get_user_pref(); // user provided volume level {0.0,1.0}

for (;;) {
    AVPacket *retrieved_pkt = get_decoded_packet_stream();  // from network stream

    AVPacket *work_pkt
       = change_volume(retrieved_pkt, volume_control); // this is what I need

    // remaining code to play the work_pkt ...
}


  



  How do I implement change_volume() or is there any off the shelf function that I can use ?

  



  Edit : Adding codec-related info as requested in the comments

  



  QAudioFormat format;
format.setFrequency(44100);
format.setChannels(2);
format.setSampleSize(16);
format.setCodec("audio/pcm");
format.setByteOrder(QAudioFormat::LittleEndian);
format.setSampleType(QAudioFormat::SignedInt);


  


• How to manipulate audio volume in ffmpeg

  24 juin 2021, par JohnTerry

  I am working on a ffmpeg command to overlay background music to a video which already has audio.

  


  below is the command -

  


      ffmpeg -i video_with_audio.webm -stream_loop -1 -i overlay_music.mp3 -vcodec copy -filter_complex amix -acodec libopus -mapping_family 0 -b:a 96k -shortest -map 0:v:0 -map 1:a:0 output_video.webm


  


  the above command is working fine but i also want to control the volume of the both audios.
so for this purpose i am using the command-

  


      cmd = "ffmpeg -i {} -filter_complex 'amovie='{}':loop=0,asetpts=N/SR/TB,volume=1[audio];[0:a]volume=3[sa];[sa][audio]amix[fa]' -map 0:v -map [fa] -vcodec copy -acodec libopus -preset ultrafast -shortest {}".format(inp_video, bg, out_video)
    os.system(cmd)


  


  but i am getting an error while passing online url-

  


    ffmpeg version n4.3.1 Copyright (c) 2000-2020 the FFmpeg developers
  built with gcc 7 (Ubuntu 7.5.0-3ubuntu1~18.04)
  configuration: --prefix= --prefix=/usr --disable-debug --disable-doc --disable-static --enable-cuda --enable-cuda-sdk --enable-cuvid --enable-libdrm --enable-ffplay --enable-gnutls --enable-gpl --enable-libass --enable-libfdk-aac --enable-libfontconfig --enable-libfreetype --enable-libmp3lame --enable-libnpp --enable-libopencore_amrnb --enable-libopencore_amrwb --enable-libopus --enable-libpulse --enable-sdl2 --enable-libspeex --enable-libtheora --enable-libtwolame --enable-libv4l2 --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libx265 --enable-libxcb --enable-libxvid --enable-nonfree --enable-nvenc --enable-omx --enable-openal --enable-opencl --enable-runtime-cpudetect --enable-shared --enable-vaapi --enable-vdpau --enable-version3 --enable-xlib
  libavutil      56. 51.100 / 56. 51.100
  libavcodec     58. 91.100 / 58. 91.100
  libavformat    58. 45.100 / 58. 45.100
  libavdevice    58. 10.100 / 58. 10.100
  libavfilter     7. 85.100 /  7. 85.100
  libswscale      5.  7.100 /  5.  7.100
  libswresample   3.  7.100 /  3.  7.100
  libpostproc    55.  7.100 / 55.  7.100
Input #0, matroska,webm, from '/home/abc/Desktop/abc/input_video.webm':
  Metadata:
    COMPATIBLE_BRANDS: isomiso2avc1mp41
    MAJOR_BRAND     : isom
    MINOR_VERSION   : 512
    ENCODER         : Lavf58.45.100
  Duration: 00:03:52.07, start: -0.007000, bitrate: 1179 kb/s
    Stream #0:0: Video: vp9 (Profile 0), yuv420p(tv), 854x480, SAR 1:1 DAR 427:240, 25 fps, 25 tbr, 1k tbn, 1k tbc (default)
    Metadata:
      HANDLER_NAME    : ISO Media file produced by Google Inc.
      ENCODER         : Lavc58.91.100 libvpx-vp9
      DURATION        : 00:03:52.007000000
    Stream #0:1: Audio: opus, 48000 Hz, stereo, fltp (default)
    Metadata:
      HANDLER_NAME    : ISO Media file produced by Google Inc.
      ENCODER         : Lavc58.91.100 libopus
      DURATION        : 00:03:52.068000000
[Parsed_amovie_0 @ 0x56189e8f9900] Failed to avformat_open_input 'https'
[AVFilterGraph @ 0x56189e947e00] Error initializing filter 'amovie' with args 'https://dapi.videowiki.pt/media/music-lib/2021/04/05/31/21/bensound-creativeminds.mp3:loop=0'
Error initializing complex filters.
No such file or directory