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• Converting DTS to AAC with ffmpeg shifts spoken audio to the right

  18 août 2018, par Giuseppe

  I am using ffmpeg to convert mkv movies to mp4, like so :

  $ ffmpeg -i source.mkv -c:v copy -c:a aac destination.mp4

  By doing this, the audio stream gets converted from the original DTS :

  Stream #0:1: Audio: dts (DTS), 48000 Hz, 5.1(side), fltp, 1536 kb/s (default)

  To AAC :

  Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, 5.1, fltp, 394 kb/s (default)

  The resulting file plays just fine, except that the spoken audio (what I am assuming would be sent to the central channel in a 5.1 configuration) sounds clearly shifted to the right, when listening through the MacBook’s built-in speakers or my stereo headphones. Note that music and other sound effects appear unaffected, properly balanced. Also note that I have been able to reproduce this behavior with a variety of source files.

  Here’s ffmpeg’s banner :

  ffmpeg version 4.0.2 Copyright (c) 2000-2018 the FFmpeg developers
  
    built with Apple LLVM version 9.1.0 (clang-902.0.39.2)
  
    configuration: --prefix=/usr/local/Cellar/ffmpeg/4.0.2 --enable-shared --enable-pthreads --enable-version3 --enable-hardcoded-tables --enable-avresample --cc=clang --host-cflags= --host-ldflags= --enable-gpl --enable-libmp3lame --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libx265 --enable-libxvid --enable-opencl --enable-videotoolbox --disable-lzma
  
    libavutil      56. 14.100 / 56. 14.100
  
    libavcodec     58. 18.100 / 58. 18.100
  
    libavformat    58. 12.100 / 58. 12.100
  
    libavdevice    58.  3.100 / 58.  3.100
  
    libavfilter     7. 16.100 /  7. 16.100
  
    libavresample   4.  0.  0 /  4.  0.  0
  
    libswscale      5.  1.100 /  5.  1.100
  
    libswresample   3.  1.100 /  3.  1.100
  
    libpostproc    55.  1.100 / 55.  1.100

• Can ffmpeg write metadata encoder when transcoding alac/flac to aac audio file ?

  11 juin 2022, par David I

  I have a collection of alac and flac files from Bandcamp and an ffmpeg instance compiled with libfdk_aac https://trac.ffmpeg.org/wiki/CompilationGuide/Centos#libfdk_aac and am trying to convert these to lossy audio aac files for non-critical listening.

  


  With ffmpeg -i Liholesie\ -\ Shamanic\ Twilight\ -\ 09\ Gray\ Wings.m4a -c:a libfdk_aac -vbr 4 -c:v copy 09_Gray_wings_vbr4.m4a an expected aac .m4a audio file is produced, album art included, works well. There's one slight detail missing :

  


  During the ffmpeg conversion process ffmpeg says :

  


  Output #0, ipod, to '09_Gray_wings_vbr4.m4a':
  Metadata:
    major_brand     : M4A 
    minor_version   : 512
    compatible_brands: M4A isomiso2
    title           : Gray Wings
    artist          : Liholesie
    album_artist    : Liholesie
    album           : Shamanic Twilight
    comment         : Visit https://liholesie.bandcamp.com
    date            : 2021
    track           : 9
    encoder         : Lavf59.24.100
  Stream #0:0: Video: mjpeg (Baseline), yuvj444p(pc, bt470bg/unknown/unknown), 700x700 [SAR 72:72 DAR 1:1], q=2-31, 90k tbr, 90k tbn (attached pic)
  Stream #0:1(und): Audio: aac (mp4a / 0x6134706D), 44100 Hz, stereo, s16 (default)
    Metadata:
      handler_name    : SoundHandler
      vendor_id       : [0][0][0][0]
      encoder         : Lavc59.33.100 libfdk_aac 
..




  


  and the file produced looks like that when ffprobed except that the Metadata : encoder field is missing :

  


  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '09_Gray_wings_vbr4.m4a':
  Metadata:
    major_brand     : M4A 
    minor_version   : 512
    compatible_brands: M4A isomiso2
    title           : Gray Wings
    artist          : Liholesie
    album_artist    : Liholesie
    album           : Shamanic Twilight
    date            : 2021
    encoder         : Lavf59.24.100
    comment         : Visit https://liholesie.bandcamp.com
    track           : 9
  Duration: 00:06:57.78, start: 0.000000, bitrate: 155 kb/s
  Stream #0:0[0x2](und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 152 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
      vendor_id       : [0][0][0][0]
  Stream #0:1[0x0]: Video: mjpeg (Baseline), yuvj444p(pc, bt470bg/unknown/unknown), 700x700 [SAR 72:72 DAR 1:1], 90k tbr, 90k tbn (attached pic)


  


  Is there a way to write the encoder field in the Metadata section when transcoding (or is "encoder" not supported for aac m4a ? That would be weird since ffmpeg says what it says when specifying output during transcoding) .

  


  Any hints on how to write a self-defined text to said tag during transcoding are also welcome.

  


• Layer black & white video over background so black pixels are transparent in FFMPEG

  4 février 2018, par Dan Weaver

  I’m trying to blend a video containing black and white animated text over a static background image. I can successfully blend them but no matter what blend mode I use I can’t get the effect I want.

  I’m looking for an effect similar to Photoshop’s ’Add’ blend mode where the color values of each pixel are added together. This results in no change where the top layer (video) has black pixels, effectively making the black background appear transparent.

  This is what I’m trying to achieve :
  

  ffmpeg -i text.mp4 -loop 1 -i image.jpg \
-filter_complex 'blend=all_mode=addition' -t 1 result.mp4

  I tried all the modes of the blend filter but none of them produce this effect. I thought Addition would be the one to work but the resulting video has a pink tint. Maybe there is some mismatch between color channels ?

  How can I get the result I’m looking for ?