The documentation and wiki imply the native AAC encoder can output CBR and VBR files : >b >Set bit rate in bits/s. Setting this automatically activates constant bit rate >(CBR) mode. If this option is unspecified it is set to 128kbps. > >q >Set quality for variable bit rate (VBR) mode. This option is valid only using >the ffmpeg command-line tool. For library interface users, use global_quality.
Sources: - https://ffmpeg.org/ffmpeg-all.html#Options-7 - https://trac.ffmpeg.org/wiki/Encode/AAC#NativeFFmpegAACEncoder But testing the CBR mode gives out unexpected results 1. `ffmpeg -f lavfi -i sine=d=10 -c:a aac -b:a 128k out.m4a` => outputs a variable bit rate file, with an average bitrate of 85kbps file, and a max bitrate of 128kbps 2. `ffmpeg -i someMusicMp3File -c:a aac -b:a 128k out.m4a` => outputs a variable bit rate file, with an average bitrate of 122kbps file, and a max bitrate of 128kbps I think the advertised "CBR" mode is instead a “constrained VBR” mode, where the provided bitrate is used as a target and/or a maximum allowed bitrate. Signed-off-by: Guillaume Khayat <guillaume.kh....@gmail.com> --- doc/encoders.texi | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff --git a/doc/encoders.texi b/doc/encoders.texi index aa3a6eeb66..44ff5e469b 100644 --- a/doc/encoders.texi +++ b/doc/encoders.texi @@ -30,17 +30,19 @@ follows. Advanced Audio Coding (AAC) encoder. -This encoder is the default AAC encoder, natively implemented into FFmpeg. +This encoder is the default AAC encoder, natively implemented into FFmpeg. It +supports a constrained variable bit rate mode and a true variable bit (VBR) +rate mode. @subsection Options @table @option @item b -Set bit rate in bits/s. Setting this automatically activates constant bit rate -(CBR) mode. If this option is unspecified it is set to 128kbps. +Set maxmimum bit rate in bits/s. Setting this automatically activates constrained +variable bit rate mode. If this option is unspecified it is set to 128kbps. @item q -Set quality for variable bit rate (VBR) mode. This option is valid only using +Set quality for true variable bit rate (VBR) mode. This option is valid only using the @command{ffmpeg} command-line tool. For library interface users, use @option{global_quality}. -- 2.24.2 (Apple Git-127) _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
