VBR Quality Minimum and Maximum Values for FFmpeg

[alexander121]

Hello,
do you know if there is a list with the minimum and maximum values of the VBR Quality parameter (-q:a) for each encoder of FFMPEG ?

What were they thinking of when they did not publish this ?

[Chris K]

AFAIK it only works for mp3. You can set it from 1-10. You can check it out on the final file size with e.g. MediaInfo. Values higher than 10 don't give any change.

[alexander121]

from my tests i found out that it also works for

aac,libvorbis,speex.

what's the point of having a parameter if it does not work for all lossy encoders.

if it does not work why don't they just print a message that this parameter does not work for this encoder !!

[Chris K]

from my tests i found out that it also works for

aac,libvorbis,speex.

How did you check that out! I tried it on AAC but didn't see any change in file size like I see with mp3.

what's the point of having a parameter if it does not work for all lossy encoders.

if it does not work why don't they just print a message that this parameter does not work for this encoder !!

FFmpeg passes through a lot without any notice that it isn't applicable on the selected codec. FFmpeg is mainly a sandbox for developers at which we are allowed to play with their built castles.

Aside from that, most audio codecs come from "third party" developers. If their code doesn't support a quality option, FFmpeg cannot offer it with the -q:a command.

Chris

[Cornucopia]

Does CABAC work for MPEG2? No. Does CRF work for MPEG1? No. Does HBR work for MP2? No.

Each type of encoder (lossy or lossless) has parameters that are particular to it, or to its class/family. Many parameters are not universal. Doesn't mean there is no point to having it available for the codec it DOES work with.

Should the documentation be better? SURE! Since those FOSS things are often volunteer efforts, why don't you agree to take that on?! No? Maybe that's because you are busy like the rest of us and have to prioritize (which is what they're doing).


Scott

[alexander121]

actually i tried again the q:a parameter and it indeed works.

the file sizes differ.

here are the results..

regarding my comments for ffmpeg i think they should charge Google more for having such a great software used by Google Chrome

c:\1>ffmpeg -i natgeo.mp4 -vn -strict -2 -c:a aac -q:a 0 a.aac
ffmpeg version N-68625-g1728659 Copyright (c) 2000-2014 the FFmpeg developers
  built on Dec 19 2014 22:02:36 with gcc 4.9.2 (GCC)
  configuration: --enable-gpl --enable-version3 --disable-w32threads --enable-av
isynth --enable-bzlib --enable-fontconfig --enable-frei0r --enable-gnutls --enab
le-iconv --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --
enable-libfreetype --enable-libgme --enable-libgsm --enable-libilbc --enable-lib
modplug --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrw
b --enable-libopenjpeg --enable-libopus --enable-librtmp --enable-libschroedinge
r --enable-libsoxr --enable-libspeex --enable-libtheora --enable-libtwolame --en
able-libvidstab --enable-libvo-aacenc --enable-libvo-amrwbenc --enable-libvorbis
 --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264 --enable-
libx265 --enable-libxavs --enable-libxvid --enable-decklink --enable-zlib
  libavutil      54. 15.100 / 54. 15.100
  libavcodec     56. 16.100 / 56. 16.100
  libavformat    56. 16.101 / 56. 16.101
  libavdevice    56.  3.100 / 56.  3.100
  libavfilter     5.  4.100 /  5.  4.100
  libswscale      3.  1.101 /  3.  1.101
  libswresample   1.  1.100 /  1.  1.100
  libpostproc    53.  3.100 / 53.  3.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'natgeo.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 1
    compatible_brands: isom
    creation_time   : 2012-07-09 11:58:52
  Duration: 00:01:00.29, start: 0.000000, bitrate: 1932 kb/s
    Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, bt709/
unknown/unknown), 720x406, 1800 kb/s, 25 fps, 25 tbr, 25k tbn, 50 tbc (default)
    Metadata:
      creation_time   : 2012-07-08 08:37:43
      handler_name    : Video
    Stream #0:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, flt
p, 128 kb/s (default)
    Metadata:
      creation_time   : 2012-07-08 08:37:49
      handler_name    : GPAC ISO Audio Handler
File 'a.aac' already exists. Overwrite ? [y/N] y
Output #0, adts, to 'a.aac':
  Metadata:
    major_brand     : isom
    minor_version   : 1
    compatible_brands: isom
    encoder         : Lavf56.16.101
    Stream #0:0(eng): Audio: aac, 48000 Hz, stereo, fltp, 128 kb/s (default)
    Metadata:
      creation_time   : 2012-07-08 08:37:49
      handler_name    : GPAC ISO Audio Handler
      encoder         : Lavc56.16.100 aac
Stream mapping:
  Stream #0:1 -> #0:0 (aac (native) -> aac (native))
Press [q] to stop, [?] for help
size=     980kB time=00:01:00.28 bitrate= 133.2kbits/s
video:0kB audio:961kB subtitle:0kB other streams:0kB global headers:0kB muxing o
verhead: 2.011527%

c:\1>dir a.aac
 Volume in drive C has no label.
 Volume Serial Number is A668-762F

 Directory of c:\1

03/03/2015  08:36 PM         1,003,569 a.aac
               1 File(s)      1,003,569 bytes
               0 Dir(s)  160,578,973,696 bytes free

c:\1>ffmpeg -i natgeo.mp4 -vn -strict -2 -c:a aac -q:a 5 a.aac
ffmpeg version N-68625-g1728659 Copyright (c) 2000-2014 the FFmpeg developers
  built on Dec 19 2014 22:02:36 with gcc 4.9.2 (GCC)
  configuration: --enable-gpl --enable-version3 --disable-w32threads --enable-av
isynth --enable-bzlib --enable-fontconfig --enable-frei0r --enable-gnutls --enab
le-iconv --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --
enable-libfreetype --enable-libgme --enable-libgsm --enable-libilbc --enable-lib
modplug --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrw
b --enable-libopenjpeg --enable-libopus --enable-librtmp --enable-libschroedinge
r --enable-libsoxr --enable-libspeex --enable-libtheora --enable-libtwolame --en
able-libvidstab --enable-libvo-aacenc --enable-libvo-amrwbenc --enable-libvorbis
 --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264 --enable-
libx265 --enable-libxavs --enable-libxvid --enable-decklink --enable-zlib
  libavutil      54. 15.100 / 54. 15.100
  libavcodec     56. 16.100 / 56. 16.100
  libavformat    56. 16.101 / 56. 16.101
  libavdevice    56.  3.100 / 56.  3.100
  libavfilter     5.  4.100 /  5.  4.100
  libswscale      3.  1.101 /  3.  1.101
  libswresample   1.  1.100 /  1.  1.100
  libpostproc    53.  3.100 / 53.  3.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'natgeo.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 1
    compatible_brands: isom
    creation_time   : 2012-07-09 11:58:52
  Duration: 00:01:00.29, start: 0.000000, bitrate: 1932 kb/s
    Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, bt709/
unknown/unknown), 720x406, 1800 kb/s, 25 fps, 25 tbr, 25k tbn, 50 tbc (default)
    Metadata:
      creation_time   : 2012-07-08 08:37:43
      handler_name    : Video
    Stream #0:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, flt
p, 128 kb/s (default)
    Metadata:
      creation_time   : 2012-07-08 08:37:49
      handler_name    : GPAC ISO Audio Handler
File 'a.aac' already exists. Overwrite ? [y/N] y
Output #0, adts, to 'a.aac':
  Metadata:
    major_brand     : isom
    minor_version   : 1
    compatible_brands: isom
    encoder         : Lavf56.16.101
    Stream #0:0(eng): Audio: aac, 48000 Hz, stereo, fltp, 128 kb/s (default)
    Metadata:
      creation_time   : 2012-07-08 08:37:49
      handler_name    : GPAC ISO Audio Handler
      encoder         : Lavc56.16.100 aac
Stream mapping:
  Stream #0:1 -> #0:0 (aac (native) -> aac (native))
Press [q] to stop, [?] for help
size=    1438kB time=00:01:00.28 bitrate= 195.4kbits/s
video:0kB audio:1419kB subtitle:0kB other streams:0kB global headers:0kB muxing
overhead: 1.362200%

c:\1>dir a.aac
 Volume in drive C has no label.
 Volume Serial Number is A668-762F

 Directory of c:\1

03/03/2015  08:37 PM         1,472,512 a.aac
               1 File(s)      1,472,512 bytes
               0 Dir(s)  160,578,494,464 bytes free

[Chris K]

actually i tried again the q:a parameter and it indeed works.

the file sizes differ.

Ok! You use the internal experimental aac encoder. Good to know it works.

I used libvo_aacenc which seems to not support this feature (unless I've missed something).

Chris