FFmpeg amerge multi input create an output with a lower volume

[wouha]

Hello,

When I use -filter_complex & amerge to merge multiple audio files into one audio file but the volume of output file is lower than what it should be! (something like 2 or 3 times lower)

My ffmpeg command:

ffmpeg -i INPUT_1 -i INPUT_2 -i INPUT_3 -i INPUT_4 i INPUT_5 -i INPUT_6 -filter_complex "
[0:a]volume=volume=1:precision=fixed:eval=frame[a0];
[1:a]volume=volume=1:precision=fixed:eval=frame[a1];
[2:a]volume=volume=1:precision=fixed:eval=frame[a2];
[3:a]volume=volume=1:precision=fixed:eval=frame[a3];
[4:a]volume=volume=1:precision=fixed:eval=frame[a4];
[5:a]volume=volume=1:precision=fixed:eval=frame[a5];
[a0][a1][a2][a3][a4][a5]amerge=inputs=6,
pan=stereo|FL<c0+c2+c4+c6+c8+c10|FR<c1+c3+c5+c7+c9+c11[aout]"
 -map "[aout]" -acodec libmp3lame -b:a 256k OUTPUT

I use FFmpeg 2.6.1 on Debian 3.2.63-2+deb7u1 x86_64

Can you help me about my problem?

Thank you a lot !

Best regards,
Max.

[Cigaes]

More precisely, it is exactly six times lower in terms of linear intensity. This is the expected behaviour. A lot of PCM hardware and software code samples in a bounded interval, usually equivalent to the [-1,1] interval after normalization. The problem is that 0.9+0.9=1.8 does not fit to the interval; you have to do an average, not a sum: (0.9+0.9)/2.

That is exactly what "FL<..." does: it is equivalent to "FL=(...)/N", where N is the number of channels you added. You are perfectly free to write "FL=c0+c2+..." instead of "FL<...". You will get normal volume but possibly clipping.

I do not remember if FFmpeg has soft-clipping filters.

[wouha]

Oh my god!
This is it!

Thank you A LOT!

[wouha]

Now there is a saturation \o/

Maybe because the volume of the input file is too loud!

Do you think I can fix this with a function of ffmpeg?

Thank you :-)

[wouha]

Problem solved by converting flac instead of mp3!

It's ok for me!

Thank you for your time! :)

Bye

[Michael Niedermayer]

remove invalid blocked by value