#10870: libfdk_aac and aac_at encoders inflate small samples, native aac encoder
doesn't
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Reporter: mrapp | Type: defect
Status: new | Priority: normal
Component: undetermined | Version: 6.1
Keywords: AAC | Blocked By:
Blocking: | Reproduced by developer: 0
Analyzed by developer: 0 |
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Summary of the bug:
Re-encoding a 192 kb/s AAC-LC stream to 128 kb/s with either the
libfdk_aac or aac_at encoders results in a stream that is 256 kb/s. The
status shows ~128 kb/s until the last few seconds, then jumps up and the
time index progresses slower. A trace confirms what is happening is in the
last couple of seconds, there are a lot more samples of smaller size. This
is probably a pathological case, but I have run across several different
videos exhibiting this issue (the audio stream originates from mp4
videos). Performing a trace on a copy command from the output of each
encoder shows that libfdk_aac and aac_at are inflating the size of these
small samples by 100 times, whereas the native aac is preserving the
original small size.
How to reproduce:
{{{
% ffmpeg -i audio.mp4 -c:a libfdk_aac -ac 2 -b:a 128k out.mp4
ffmpeg version 4.4.4 and 6.1
built on macOS 11.7.10 using MacPorts:
$ ffmpeg6 -version
ffmpeg version 6.1 Copyright (c) 2000-2023 the FFmpeg developers
built with Apple clang version 13.0.0 (clang-1300.0.29.30)
configuration: --cc=/usr/bin/clang
--datadir=/opt/local/libexec/ffmpeg6/share/data
--docdir=/opt/local/libexec/ffmpeg6/share/doc --progs-suffix=6
--prefix=/opt/local/libexec/ffmpeg6 --enable-audiotoolbox --disable-
indev=jack --disable-libjack --disable-libopencore-amrnb --disable-
libopencore-amrwb --disable-libxcb --disable-libxcb-shm --disable-libxcb-
xfixes --disable-metal --disable-outdev=xv --enable-opencl --enable-sdl2
--disable-securetransport --enable-videotoolbox --disable-xlib --enable-
avfilter --enable-fontconfig --enable-gnutls --enable-libass --enable-
libbluray --enable-libdav1d --enable-libfreetype --enable-libfribidi
--enable-libmodplug --enable-libmp3lame --enable-libopenjpeg --enable-
libopus --enable-librsvg --enable-libsoxr --enable-libspeex --enable-
libtheora --enable-libvorbis --enable-libvpx --enable-libzimg --enable-
libzvbi --enable-lzma --enable-shared --enable-pthreads --enable-swscale
--enable-zlib --enable-libaom --enable-libsvtav1 --arch=arm64 --enable-
librtmp --enable-gpl --enable-libvidstab --enable-libx264 --enable-libx265
--enable-libxvid --enable-postproc --enable-libfdk-aac --enable-nonfree
libavutil 58. 29.100 / 58. 29.100
libavcodec 60. 31.102 / 60. 31.102
libavformat 60. 16.100 / 60. 16.100
libavdevice 60. 3.100 / 60. 3.100
libavfilter 9. 12.100 / 9. 12.100
libswscale 7. 5.100 / 7. 5.100
libswresample 4. 12.100 / 4. 12.100
libpostproc 57. 3.100 / 57. 3.100
ffmpeg version 4.4.4 Copyright (c) 2000-2023 the FFmpeg developers
built with Apple clang version 13.0.0 (clang-1300.0.29.30)
configuration: --prefix=/opt/local --cc=/usr/bin/clang
--mandir=/opt/local/share/man --enable-audiotoolbox --disable-indev=jack
--disable-libjack --disable-libopencore-amrnb --disable-libopencore-amrwb
--disable-libxcb --disable-libxcb-shm --disable-libxcb-xfixes --enable-
opencl --disable-outdev=xv --enable-sdl2 --disable-securetransport
--enable-videotoolbox --enable-avfilter --enable-avresample --enable-
fontconfig --enable-gnutls --enable-libass --enable-libbluray --enable-
libdav1d --enable-libfreetype --enable-libfribidi --enable-libmodplug
--enable-libmp3lame --enable-libopenjpeg --enable-libopus --enable-librsvg
--enable-libsoxr --enable-libspeex --enable-libtheora --enable-libvorbis
--enable-libvpx --enable-libzimg --enable-libzvbi --enable-lzma --enable-
pthreads --enable-shared --enable-swscale --enable-zlib --enable-libaom
--enable-libsvtav1 --arch=arm64 --enable-librtmp --enable-gpl --enable-
libvidstab --enable-libx264 --enable-libx265 --enable-libxvid --enable-
postproc --enable-libfdk-aac --enable-nonfree
libavutil 56. 70.100 / 56. 70.100
libavcodec 58.134.100 / 58.134.100
libavformat 58. 76.100 / 58. 76.100
libavdevice 58. 13.100 / 58. 13.100
libavfilter 7.110.100 / 7.110.100
libavresample 4. 0. 0 / 4. 0. 0
libswscale 5. 9.100 / 5. 9.100
libswresample 3. 9.100 / 3. 9.100
libpostproc 55. 9.100 / 55. 9.100
}}}
--
Ticket URL: <https://trac.ffmpeg.org/ticket/10870>
FFmpeg <https://ffmpeg.org>
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