On 28-04-2024 12:44, Aditya Dandavate wrote:
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
Well, the warning is not from ffmpeg but from libfdk_aac and this is the
reason:
"As of FDK version 3.4.12, not all combinations of audio object
types, bitrate modes, channel layouts, and sample rates can be used
together, due to a limited table of pre-computed values used by the
encoder. For example, using 96kHz stereo input with the AAC-LC audio
object type and bitrate mode 5 (VBR 96-112kbps/channel) will result in
catastrophic failure"
There has been a patch to (partly) resolve this, but it still has
limits, hence the warning.
Also, VBR 1-4 can only be used with specific (low) sampling rates, only
5 can be used for samplerates >15 kHz
Fraunhofer does not recommend using VBR with this codec.
Generally, if your device supports the Opus codec, use that, it has
(much) better quality at the same bitrate as AAC, or much smaller files
with the same quality as AAC
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