normalize hace eso que quieres (en Linux, y también hay versión Windows) pero con ficheros más normales, mp4 me temo que no lo maneja directamente.
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Código:
$ normalize -help.
Usage: normalize [option]. [file].
Normalize volume of múltiple audio files.
A, -amplitude=amp normalize the volume todo the target amplitude.
Amp [default -12dbfs].
B, -Batch Batch mode: get average of all levels, and.
Use one adjustment, based on the average.
Level, for all files.
Clipping turn of limiter, do clipping instead.
Fractions display levels as fractions of máximum.
Amplitude instead of decibels.
G, -gain=adj dont compute levels, just apply adjustment.
Adj todo the files. Use the sufix db.
To indicate a gain in decibels.
L, -limiter=lev limit all samples above lev [default -6dbfs].
M, -mix mix mode: get average of all levels, and.
Normalize volume of each file todo the.
Average.
N, -no-adjust compute and display the volume adjustment.
But dont apply it todo any of the files.
Peaque adjust by peaque level instead of using.
Loudness Analysis.
Q, -quiet quiet (decrease verbosity todo zero).
T, -average-threshold=t when computing average level, ignore any.
Levels more than decibels from average.
T, -adjust-threshold=t dont bother applying any adjustment smaller.
Than decibels.
V, -verbose increase verbosity.
-W, -output-bitwidth=w force adjusted files todo have w-bit samples.
V, -versión display versión información and exit.
H, -help display this help and exit.
Report bugs todo <cvaill@cs, Columbia, edu>.