[FFmpeg-trac] #7550(undetermined:new): Audible artifacts when converting from WAV to AAC

FFmpeg trac at avcodec.org
Sat Nov 17 14:53:05 EET 2018


#7550: Audible artifacts when converting from WAV to AAC
-------------------------------------+-------------------------------------
             Reporter:  sleroux      |                     Type:  defect
               Status:  new          |                 Priority:  normal
            Component:               |                  Version:  git-
  undetermined                       |  master
             Keywords:               |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
-------------------------------------+-------------------------------------
 While converting a WAV file to AAC I noticed audible audio artifacts.
 Especially, the artifacts seem to appear on only one channel even in dual-
 mono.

 The issue has improved in the latest build compared to ffmpeg
 3.2.12-1~deb9u1 used on our Debian 9.4 production host but is still
 clearly audible.

 A particularly audible artifact is present between 00:05:30.930 and
 00:05:30.940 is the attached example file. I copied the audio files in
 extenso since the artifact seems to vanish when I trim the input file.


 Attached:

 * EP26-wav-to-aac-artifacts-orig.wav : the original uncompressed audio
 file
 * EP26-wav-to-aac-artifacts-ffmpeg-debian-stable.mp4 : the audio
 transcoded as AAC by ffmpeg 3.2.12-1~deb9u1 on our Debian 9.4 production
 host
 * EP26-wav-to-aac-artifacts-ffmpeg-static-latest.mp4 : the audio
 transcoded as AAC by the latest ffmpeg static build
 * Audacity screen capture pinpointing an artifact (first stereo pair is
 original WAV, second stereo pair is output produced by ffmpeg on Debian
 9.4, third stereo pair in output produced by the lattest ffmpeg static
 build)


 How to reproduce:
 {{{
 $ /tmp/ffmpeg-git-20181115-amd64-static/ffmpeg -i EP26-wav-to-aac-
 artifacts-orig.wav -c:a aac EP26-wav-to-aac-artifacts-ffmpeg-debian-
 stable.mp4
 ffmpeg version N-47455-g1096614c42-static
 https://johnvansickle.com/ffmpeg/  Copyright (c) 2000-2018 the FFmpeg
 developers
   built with gcc 6.3.0 (Debian 6.3.0-18+deb9u1) 20170516
   configuration: --enable-gpl --enable-version3 --enable-static --disable-
 debug --disable-ffplay --disable-indev=sndio --disable-outdev=sndio
 --cc=gcc-6 --enable-fontconfig --enable-frei0r --enable-gnutls --enable-
 gray --enable-libaom --enable-libfribidi --enable-libass --enable-libvmaf
 --enable-libfreetype --enable-libmp3lame --enable-libopencore-amrnb
 --enable-libopencore-amrwb --enable-libopenjpeg --enable-librubberband
 --enable-libsoxr --enable-libspeex --enable-libvorbis --enable-libopus
 --enable-libtheora --enable-libvidstab --enable-libvo-amrwbenc --enable-
 libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2
 --enable-libxvid --enable-libzimg
   libavutil      56. 23.101 / 56. 23.101
   libavcodec     58. 39.100 / 58. 39.100
   libavformat    58. 22.100 / 58. 22.100
   libavdevice    58.  6.100 / 58.  6.100
   libavfilter     7. 43.100 /  7. 43.100
   libswscale      5.  4.100 /  5.  4.100
   libswresample   3.  4.100 /  3.  4.100
   libpostproc    55.  4.100 / 55.  4.100
 Guessed Channel Layout for Input Stream #0.0 : stereo
 Input #0, wav, from 'EP26-wav-to-aac-artifacts-orig.wav':
   Duration: 00:07:46.24, bitrate: 1536 kb/s
     Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 48000 Hz,
 stereo, s16, 1536 kb/s
 Stream mapping:
   Stream #0:0 -> #0:0 (pcm_s16le (native) -> aac (native))
 Press [q] to stop, [?] for help
 Output #0, mp4, to 'EP26-wav-to-aac-artifacts-ffmpeg-debian-stable-2.mp4':
   Metadata:
     encoder         : Lavf58.22.100
     Stream #0:0: Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo,
 fltp, 128 kb/s
     Metadata:
       encoder         : Lavc58.39.100 aac
 size=    6513kB time=00:07:46.24 bitrate= 114.4kbits/s speed=36.3x
 video:0kB audio:6427kB subtitle:0kB other streams:0kB global headers:0kB
 muxing overhead: 1.342028%
 [aac @ 0x55cedc0] Qavg: 15720.868
 }}}

--
Ticket URL: <https://trac.ffmpeg.org/ticket/7550>
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