[FFmpeg-user] vbr with libfdk_aac ?

[Timothy Gu]

On Thu, Apr 18, 2013 at 11:57 AM, sean darcy <seandarcy2 at gmail.com> wrote:
> ffmpeg -i 17.wav -vn -c:a libfdk_aac -vbr 2 -afterburner 1 17.m4a
> ffmpeg version N-52058-g423089e Copyright (c) 2000-2013 the FFmpeg
> developers
>   built on Apr 13 2013 19:19:37 with gcc 4.7.2 (GCC) 20120921 (Red Hat
> 4.7.2-2)
>   configuration: --prefix=/usr --bindir=/usr/bin --datadir=/usr/share/ffmpeg
> --incdir=/usr/include/ffmpeg --libdir=/usr/lib64 --mandir=/usr/share/man
> --arch=x86_64 --cpu=amdfam10 --optflags='-Ofast -march=native -mtune=native
> -fopenmp -fomit-frame-pointer -pipe -fPIC' --enable-avresample
> --enable-libopencore-amrnb --enable-libopencore-amrwb
> --enable-libvo-amrwbenc --enable-version3 --enable-bzlib --disable-crystalhd
> --enable-frei0r --enable-libfdk-aac --enable-gnutls --enable-libass
> --enable-libcdio --enable-libcelt --enable-libdc1394 --disable-indev=jack
> --enable-libfreetype --enable-libgsm --enable-libmp3lame --enable-openal
> --enable-libopencv --enable-libopenjpeg --enable-libopus --enable-libpulse
> --enable-librtmp --enable-libschroedinger --enable-libspeex
> --enable-libtheora --enable-libvorbis --enable-libv4l2 --enable-libvpx
> --enable-libx264 --enable-libxvid --enable-x11grab --enable-avfilter
> --enable-postproc --enable-pthreads --disable-static --enable-shared
> --enable-gpl --enable-nonfree --enable-zlib   libavutil      52. 26.100 /
> 52. 26.100
>   libavcodec     55.  2.100 / 55.  2.100
>   libavformat    55.  2.100 / 55.  2.100
>   libavdevice    55.  0.100 / 55.  0.100
>   libavfilter     3. 53.101 /  3. 53.101
>   libavresample   1.  1.  0 /  1.  1.  0
>   libswscale      2.  2.100 /  2.  2.100
>   libswresample   0. 17.102 / 0. 17.102
>   libpostproc    52.  3.100 / 52.  3.100
> [wav @ 0xe1ba00] max_analyze_duration 5000000 reached at 5015510
> microseconds
> Guessed Channel Layout for  Input Stream #0.0 : stereo
> Input #0, wav, from '17.wav':
>   Duration: 00:30:31.07, bitrate: 1411 kb/s
>     Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 44100 Hz, stereo,
> s16, 1411 kb/s
> [libfdk_aac @ 0xe43280] Note, the VBR setting is unsupported and only works
> with some parameter combinations

Question for Sean:

Is the output OK? If it is, then it shouldn't be a problem. (Also see
question a) below)

I also have a couple of questions for developers for the library.
Please correct me (and please don't consider me rude) if I am wrong.

a) According to the official libfdk-aac available in mstorsjo's repo,
it does not say anything about VBR, or values between 1-5 for param
AACENC_BITRATEMODE. But in line 185 of libavcodec/libfdk-aacenc.c,
ffmpeg is setting it for VBR. In my opinion, not say it can do VBR
stuff means it can't.

b) Shouldn't -vbr be -q:a? And if it is for abbreviating "-flags
+qscale -global_quality [1-5]", shouldn't it also map to other codecs
requiring this option?

Timothy G.