[FFmpeg-user] Why is there a Guide on libfdk_aac VBR AAC when it is not supported and working?

[bat guano]

----------------------------------------
 My used combination LC-AAC 2ch 48000 1,2,3,4,5
> is also in the table. After the transcoding the result is flagged as 'CBR',
> in stead of VBR...

Hi
Maybe that's a problem with how FFmpeg uses fdk_aac.


@ubuntu:~$ fdkaac -m 3 -o test1.m4a foo.wav
[100%] 00:30.071/00:30.071 (6x), ETA 00:00.000   
1443389/1443389 samples processed in 00:04.709

@ubuntu:~$ mediainfo test1.m4a
General
Complete name                            : test1.m4a
Format                                   : MPEG-4
Format profile                           : Apple audio with iTunes info
Codec ID                                 : M4A 
File size                                : 562 KiB
Duration                                 : 30s 123ms
Overall bit rate mode                    : Variable
Overall bit rate                         : 153 Kbps
Encoded date                             : UTC 2013-02-20 19:49:47
Tagged date                              : UTC 2013-02-20 19:49:47
Writing application                      : fdkaac 0.1.5, libfdk-aac 3.3.3, VBR mode 3

Audio
ID                                       : 1
Format                                   : AAC
Format/Info                              : Advanced Audio Codec
Format profile                           : LC
Codec ID                                 : 40
Duration                                 : 30s 123ms
Bit rate mode                            : Variable
Bit rate                                 : 151 Kbps
Maximum bit rate                         : 213 Kbps
Channel(s)                               : 2 channels
Channel positions                        : Front: L R
Sampling rate                            : 48.0 KHz
Compression mode                         : Lossy
Stream size                              : 555 KiB (99%)
Encoded date                             : UTC 2013-02-20 19:49:47
Tagged date                              : UTC 2013-02-20 19:49:47


@ubuntu:~$ ffmpeg -i foo.wav -c:a libfdk_aac -vbr 3 test2.m4a
ffmpeg version git-2013-01-22-766f055 Copyright (c) 2000-2013 the FFmpeg developers
  built on Jan 22 2013 14:16:03 with gcc 4.5.2 (Ubuntu/Linaro 4.5.2-8ubuntu4)
  configuration: --enable-gpl --enable-libaacplus --enable-libfaac --enable-libfdk-aac --enable-libilbc --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopus --enable-librtmp --enable-libspeex --enable-libtheora --enable-libvo-aacenc --enable-libvo-amrwbenc --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libxvid --enable-nonfree --enable-version3 --enable-x11grab
  libavutil      52. 15.100 / 52. 15.100
  libavcodec     54. 90.100 / 54. 90.100
  libavformat    54. 61.102 / 54. 61.102
  libavdevice    54.  3.102 / 54.  3.102
  libavfilter     3. 33.100 /  3. 33.100
  libswscale      2.  2.100 /  2.  2.100
  libswresample   0. 17.102 /  0. 17.102
  libpostproc    52.  2.100 / 52.  2.100
[wav @ 0xb3c7320] max_analyze_duration 5000000 reached at 5013333 microseconds
Guessed Channel Layout for  Input Stream #0.0 : stereo
Input #0, wav, from 'foo.wav':
  Metadata:
    artist          : Jody Marie Gnant
    copyright       : 1995 Sirius Publishing
    title           : Lucky Night
    encoder         : Lavf54.61.102
  Duration: 00:00:30.07, bitrate: 1536 kb/s
    Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 48000 Hz, stereo, s16, 1536 kb/s
[libfdk_aac @ 0xb4be580] Note, the VBR setting is unsupported and only works with some parameter combinations
Output #0, ipod, to 'test2.m4a':
  Metadata:
    artist          : Jody Marie Gnant
    copyright       : 1995 Sirius Publishing
    title           : Lucky Night
    encoder         : Lavf54.61.102
    Stream #0:0: Audio: aac (mp4a / 0x6134706D), 48000 Hz, stereo, s16
Stream mapping:
  Stream #0:0 -> #0:0 (pcm_s16le -> libfdk_aac)
Press [q] to stop, [?] for help
size=     561kB time=00:00:30.08 bitrate= 152.8kbits/s    
video:0kB audio:555kB subtitle:0 global headers:0kB muxing overhead 1.146276%

@ubuntu:~$ mediainfo test2.m4a
General
Complete name                            : test2.m4a
Format                                   : MPEG-4
Format profile                           : Apple audio with iTunes info
Codec ID                                 : M4A 
File size                                : 561 KiB
Duration                                 : 30s 114ms
Overall bit rate mode                    : Constant
Overall bit rate                         : 153 Kbps
Track name                               : Lucky Night
Performer                                : Jody Marie Gnant
Writing application                      : Lavf54.61.102
Copyright                                : 1995 Sirius Publishing

Audio
ID                                       : 1
Format                                   : AAC
Format/Info                              : Advanced Audio Codec
Format profile                           : LC
Codec ID                                 : 40
Duration                                 : 30s 114ms
Duration_LastFrame                       : -9ms
Bit rate mode                            : Constant
Bit rate                                 : 151 Kbps
Channel(s)                               : 2 channels
Channel positions                        : Front: L R
Sampling rate                            : 48.0 KHz
Compression mode                         : Lossy
Stream size                              : 555 KiB (99%)