Newest 'ffmpeg' Questions - Stack Overflow

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• How to initialize video decoder with a already decoded frame ?

  27 mars, par Ragdoll Car

  Let's say I have an FFmpeg video decoder x264 initially initialized with some parameters. I am using C++ in my scenario. In normal conditions we push an encoded I-frame into such decoder and then referencing encoded P-frames.

  I have a special case where my I-frame is already decoded. So in my case I want to:

  • push already decoded I-frame into my decoder
  • push referencing encoded P-frames into my decoder

  How can I initialize the decoder state with already decoded I-frame? Currently to bypass these limitations I have to:

  • create a new temporary encoder
  • encode already decoded I-frame
  • decode encoded I-frame
  • and then I am able to push referencing encoded P-frames

• Audio delay after resuming FFmpeg on Windows

  27 mars, par Iman Sajadpur

  I'm building a screen recording software for Windows using Python. I use FFmpeg for recording and psutil to pause and resume the process.

  Here is a sample of my code:

  import psutil
  import subprocess
  
  process = subprocess.Popen([
          'ffmpeg', '-y',
          '-rtbufsize', '100M',
          '-f', 'gdigrab',
          '-thread_queue_size', '1024',
          '-probesize', '50M',
          '-r', '24',
          '-draw_mouse', '1',
          '-video_size', '1920x1080',
          '-i', 'desktop', 
          '-f', 'dshow',
          '-channel_layout', 'stereo',
          '-thread_queue_size', '1024',
          '-i', 'audio=Microphone (2- High Definition Audio Device)', # my audio device
          '-c:v', 'h264_nvenc', # encoding via Nvidia
          '-r', '24',
          '-preset', 'p1',
          '-pix_fmt', 'yuv444p',
          '-fps_mode', 'cfr',
          '-c:a', 'aac', 
          '-ac', '2',
          '-b:a', '128k',
          'output.mp4'])
  
  ffmpeg_proc = psutil.Process(process.pid)
  
  # pause
  ffmpeg_proc.suspend()
  
  # resume
  ffmpeg_proc.resume() 
  

  The issue is that after resuming, the audio becomes choppy and delayed, while the video continues smoothly.

  I have tried using following flags, but they didn't solve the issue:

  -analyzeduration
  -fflags +genpts
  -async
  -use_wallclock_as_timestamps
  -af aresample=async=1
  

  How can I properly pause and resume FFmpeg without causing audio delay? Is there any other method to handle this properly?

  Thanks for any suggestions.

• using FFMPEG with silencedetect to remove audio silence

  27 mars, par Zahlii

  I am trying to use the following command with the latest ffmpeg build to remove silence from my .mp3 files:

  ffmpeg -i SILENCE.mp3 -af silencedetect=n=-50dB:d=1 -y -ab 192k  SILENCE_OUT.mp3
  

  However, the following output is produced:

  ffmpeg version N-66154-g1654ca7 Copyright (c) 2000-2014 the FFmpeg developers
    built on Sep  5 2014 22:10:38 with gcc 4.8.3 (GCC)
    configuration: --enable-gpl --enable-version3 --disable-w32threads --enable-av
  isynth --enable-bzlib --enable-fontconfig --enable-frei0r --enable-gnutls --enab
  le-iconv --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --
  enable-libfreetype --enable-libgme --enable-libgsm --enable-libilbc --enable-lib
  modplug --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrw
  b --enable-libopenjpeg --enable-libopus --enable-librtmp --enable-libschroedinge
  r --enable-libsoxr --enable-libspeex --enable-libtheora --enable-libtwolame --en
  able-libvidstab --enable-libvo-aacenc --enable-libvo-amrwbenc --enable-libvorbis
   --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264 --enable-
  libx265 --enable-libxavs --enable-libxvid --enable-decklink --enable-zlib
    libavutil      54.  7.100 / 54.  7.100
    libavcodec     56.  1.100 / 56.  1.100
    libavformat    56.  4.100 / 56.  4.100
    libavdevice    56.  0.100 / 56.  0.100
    libavfilter     5.  1.100 /  5.  1.100
    libswscale      3.  0.100 /  3.  0.100
    libswresample   1.  1.100 /  1.  1.100
    libpostproc    53.  0.100 / 53.  0.100
  Input #0, mp3, from 'SILENCE.mp3':
    Metadata:
      title           : Snowblind (Featuring Tasha Baxter)
      artist          : Au5
      album           : Snowblind (Featuring Tasha Baxter)
      genre           : Electronica
      performer       : Au5
      track           : 1/1
      date            : 2014
      album_artist    : Au5,Tasha Baxter
      major_brand     : mp42
      minor_version   : 0
      compatible_brands: isommp42
      encoder         : Lavf55.42.100
    Duration: 00:05:50.80, start: 0.025057, bitrate: 192 kb/s
      Stream #0:0: Audio: mp3, 44100 Hz, stereo, s16p, 192 kb/s
  Output #0, mp3, to 'SILENCE_OUT.mp3':
    Metadata:
      TIT2            : Snowblind (Featuring Tasha Baxter)
      TPE1            : Au5
      TALB            : Snowblind (Featuring Tasha Baxter)
      TCON            : Electronica
      TPE3            : Au5
      TRCK            : 1/1
      TDRL            : 2014
      TPE2            : Au5,Tasha Baxter
      major_brand     : mp42
      minor_version   : 0
      compatible_brands: isommp42
      TSSE            : Lavf56.4.100
      Stream #0:0: Audio: mp3 (libmp3lame), 44100 Hz, stereo, s16p, 192 kb/s
      Metadata:
        encoder         : Lavc56.1.100 libmp3lame
  Stream mapping:
    Stream #0:0 -> #0:0 (mp3 (native) -> mp3 (libmp3lame))
  Press [q] to stop, [?] for help
  [silencedetect @ 0000000004398f40] silence_start: -0.00628118
  [silencedetect @ 0000000004398f40] silence_end: 3.21413 | silence_duration: 3.22
  041
  [silencedetect @ 0000000004398f40] silence_start: 343.844
  [libmp3lame @ 00000000043b2940] Trying to remove 1152 samples, but the queue is
  empty
  size=    8223kB time=00:05:50.79 bitrate= 192.0kbits/s
  video:0kB audio:8222kB subtitle:0kB other streams:0kB global headers:0kB muxing
  overhead: 0.011485%
  

  The generated audio file however still has the original length without any silence removed. See the following images:

  Any help is appreciated!

  EDIT: Alright, silence detect is only DETECTING the silence. Not removing it. I will try to post a solution for this.

• How can I remove silence from an MP3 programmatically ?

  27 mars, par Benjamin Oakes

  I have MP3 files that sometimes have silence at the end. I would like to remove this silence automatically. From what I can tell, it is "perfect" silence (0 amplitude), not background noise. The length of the content and the silence varies.

  I found some other questions about cropping to the first 30 seconds or cropping to X and X+N seconds using ffmpeg. I would think I could use a similar approach, as long as I have a way to find when the silence starts. How would I do that programatically?

  For example, one possible solution would be to have a command that finds the beginning of the "silence". I'd expect a sequence like this

  end=$(ffmpeg some-command-to-find-start-of-silence)
  ffmpeg -t "$end" -acodec copy -i inputfile.mp3 outputfile.mp3
  

  The solution does not have to use ffmpeg, but it does need to be available on Ubuntu.

• Rewrite video with ffmpeg with given non-equidistant times for each frame

  27 mars, par Aleph0

  In one of my projects it is necessary to synchronize a video with a different datasource. I already have the video as a mts file.

  I also exactly know which frame will be displayed at which time. This times are not necessarily equidistant.

  For simplicity assume that my video consists just out of 5 frames:

  Frame No	Time
  1	1s
  2	3s
  3	5s
  4	8s
  5	12s

  What kind of ffmpeg command using a list of times give by a simple text file can be used to create a video stream with non-equidistant frames with the given times.