[FFmpeg-user] VBR encoding not supported ???

[Aditya Dandavate]

I was converting flac audio to aac_lc with libfdk_aac with VBR encoding.
But I saw a message about VBR encoding.

The command and output of the command is as follows :

Command :

ffmpeg.exe -i input.flac -c:a libfdk_aac -afterburner 1 -frame_length 1024
-cutoff 0 -vbr 5 -profile:a aac_low output.m4a°

Output :

F:\DSDA-Doom>ffmpeg.exe -i input.flac -c:a libfdk_aac -afterburner 1
-cutoff 0 -frame_length 1024 -profile:a aac_low -vbr 5 output.m4a
ffmpeg version N-115010-ga2cdb2f5be Copyright (c) 2000-2024 the FFmpeg
developers
  built with gcc 13.2.0 (Rev6, Built by MSYS2 project)
  configuration:  --pkg-config=pkgconf --cc='ccache gcc' --cxx='ccache
g++' --ld='ccache g++' --extra-cxxflags=-fpermissive
--extra-cflags=-Wno-int-conversion --disable-autodetect
--enable-libopus --enable-libvorbis --enable-libx264 --enable-libx265
--enable-libaom --disable-debug --enable-libfdk-aac --enable-schannel
--enable-gpl --enable-nonfree
  libavutil      59. 16.101 / 59. 16.101
  libavcodec     61.  5.103 / 61.  5.103
  libavformat    61.  3.103 / 61.  3.103
  libavdevice    61.  2.100 / 61.  2.100
  libavfilter    10.  2.101 / 10.  2.101
  libswscale      8.  2.100 /  8.  2.100
  libswresample   5.  2.100 /  5.  2.100
  libpostproc    58.  2.100 / 58.  2.100
Input #0, flac, from 'input.flac':
  Metadata:
    encoder         : Lavf61.3.103
  Duration: 02:05:52.13, start: 0.000000, bitrate: 621 kb/s
  Stream #0:0: Audio: flac, 48000 Hz, stereo, s16
Stream mapping:
  Stream #0:0 -> #0:0 (flac (native) -> aac (libfdk_aac))
Press [q] to stop, [?] for help
[libfdk_aac @ 000001b9623d7400] *Note, the VBR setting is unsupported
and only works with some parameter combinations*
Output #0, ipod, to 'output.m4a':
  Metadata:
    encoder         : Lavf61.3.103
  Stream #0:0: Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, s16
      Metadata:
        encoder         : Lavc61.5.103 libfdk_aac
[out#0/ipod @ 000001b962402280] video:0KiB audio:229238KiB
subtitle:0KiB other streams:0KiB global headers:0KiB muxing overhead:
0.605099%
size=  230625KiB time=02:05:52.13 bitrate= 250.2kbits/s speed=18.1x

F:\DSDA-Doom>pause
Press any key to continue . . .


So, may I know what's wrong with VBR to the point its unsupported ? Is
it going to be removed in the future from the encoder ? Is it
considered experimental or stable ?


Please tell me about this 🙏


Thanks