Tell ffmpeg to use (almost) the same (audio) quality as original source?

[pxstein]

Assume I want (have to) re-encode (wiht MP3) the audio part of an original video. I can do it by flags like:

ffmpeg -i .... -acodec mp3 -ab 128 ...

or

ffmpeg -i .... libmp3lame -aq 5 ....

Ok, but this way I define the output quality independently from the existing audio quality.
Is there a way to tell ffmpeg:

"Hey ffmpeg, I don't know the exact audio source quality but find out by yourself and auto-adjust
the target audio quality by yourself so that the quality loss is minimal" ?

As far as I know there was a flag like "-sameq" in the past but this seems to be deprecated/removed in newer versions of ffmpeg.

Is there a corresponding new flag for that?

Is there a corresponding new flag for video part (Xvid codec) as well?

Thank you
Peter

[AlanHK]

May not be what you mean, but you can use the "copy" codec to have ffmpeg extract the audio from a video, basically just demuxing it, no conversion made.
e.g., (assuming the video uses AAC audio)

ffmpeg -i %1 -vn -acodec copy %1.aac

But if you're changing the audio codec, you do need to specify a bitrate, as there isn't a universal rule for equivalent bitrates in different codecs.

[Baldrick]

Sameq was just same quantizers if you converted between same codecs, see http://ffmpeg.org/trac/ffmpeg/wiki/Option%20'-sameq'%20does%20NOT%20mean%20'same%20quality''

[roberto32]

I did ffmpeg -i Ramble_On__It_Might_Get_Loud.flv -vn -acodec Ramble_On__It_Might_Get_Loud.mp3 and it says I must specify at least one output file???? when I put copy after -acodec terminal says: Could not write header for output file #0 (incorrect codec parameters ?): Invalid argument

[AlanHK]

I did ffmpeg -i Ramble_On__It_Might_Get_Loud.flv -vn -acodec Ramble_On__It_Might_Get_Loud.mp3 and it says I must specify at least one output file???? when I put copy after -acodec terminal says: Could not write header for output file #0 (incorrect codec parameters ?): Invalid argument

You specify the audio codec by: "-acodec XXX".
In your original line line the XXX is "Ramble_On__It_Might_Get_Loud.mp3" which of course isn't a codec, and so then there is no output file either.
-acodec copy
is the same as the input.
Are you sure your flv is MP3 audio?
A lot are AAC.

Do just
ffmpeg -i Ramble_On__It_Might_Get_Loud.flv
and it will tell you what video and audio codecs the file has.

[roberto32]

yeah thanks it's aac, so i'll convert it into aac but is there an option to convert aac-mp3 with "same" bitrate or like the mp3 eqivalent of particular aac

[roberto32]

I did ffmpeg -i $f -acodec copy $f.mp3 , it creates file but that file won't play and amarok says it's null....

[roberto32]

cd /media/data/robert/Videos/nekonvert
while IFS= read -r line; do  ## line is stored in $line .. len nepozna -r =recursive 

fname="${line%.*}" 
e="${line##*.}" #extension
echo "$fname"
echo "$e"

case "$e" in 
mp4)
ffmpeg -i $line -vn -acodec copy $fname.mp3
#ffmpeg -i $line -vn -acodec $fname.mp3
;;   #konci moznost pre mp4

flv) 
ffmpeg -i $line -vn -acodec copy $fname.aac
#ffmpeg -i $line -vn -acodec $fname.aac

esac #case ends

done < /media/data/robert/Videos/nekonvert/obsah.txt

it creates an mp3/aac file with same name but won't play and amarok says it's null. I read output of that script and files were converting it looks OK. Original files are in nekonvert folder, and the fielnames are in obsah.txt

[AlanHK]

I did ffmpeg -i $f -acodec copy $f.mp3 , it creates file but that file won't play and amarok says it's null....

I think you're using a Unix shell script, so I can't test it directly.
But it looks like it assumes that mp4 all have mp3 audio, which is not true.

That will create a file with the extension mp3, but won't make any conversion, it will just copy the original codec. So if it wasn't already MP3, it won't work.