[FFmpeg-user] MP3 enconding bitrate
Carl Eugen Hoyos
cehoyos at ag.or.at
Sat Oct 25 14:09:42 CEST 2014
Paulo Fidalgo <paulo.fidalgo.pt <at> gmail.com> writes:
> I have trouble to get the mp3 encoded right to play
> on my Volvo Infotainment System (Sensus 3.0), so I
> have contacted the costumer support, and they told
> me that the files are being encoding with frames
> with more than 320Kbps of bitrate.
Please ask them to explain which frame has >320kb, I
don't think it's true, see below.
> Since I don't have a tool to debug it, I've tried to
> see in codec statistics in VLC, which for the files
> I'm showing as example I've seen 380Kbps near 3:31
I played the encoded file you uploaded with vlc,
it does not show a bitrate of >320 here at any
I then analyzed the file you uploaded:
$ ffmpeg -i outff.mp3 -acodec copy -f image2 -map 0 out%5d
The largest mp3 frame in your encoded file is 960 bytes
which corresponds to 320kb/s.
Maybe you should test the following to verify:
$ lame -b 320 input.wav out320.mp3
$ lame -b 256 input.wav out256.mp3
Do both files play in your car?
Or only the second?
> I believe it's a bug on ffmpeg, although I'm not sure,
> so I'm asking for advice here, since encoding with the
> lame it works like a charm.
lame documentation states that the default for lame's
-q option is 5 but if you use -V, the default is lower
(4 or smaller for your input sample).
This may be a bug, either in the documentation of
FFmpeg (because it states that FFmpeg's option -q
corresponds to -V which is mostly does but not exactly)
or because FFmpeg sets lame's -q to 5 if you don't
specify anything else.
> I've encoded with this command:
> ffmpeg -i 2L38_01_96kHz.flac -codec:a libmp3lame
> -qscale:a 0 2L38_01_96kHz.mp3
Please test with -compression_level 4, this should
produce output files more similar with lame.
More information about the ffmpeg-user