in order to preserve best audio quality

instead of converting audio, it is better (better audio quality and also faster) to simply extract the aac from an mp4 like this:

vim /scripts/
# :) ffmpeg rocks!
if [ -z "$1" ]
	echo "=== no parameter passed will extract audio from all files in current dir ==="
	for FILE in *.mp4 ; do
		ffmpeg -i "$FILE" -vn -acodec copy "$FILE.aac"

	echo "=== parameter passed will extract audio from mp4==="
	ffmpeg -i "$1" -vn -acodec copy "$1".aac


chmod +x /scripts/

/scripts/ "File.mp4"

# the File.aac will be output into the same directory

about aac:

“Unlike MPEG Layer 3 (MP3), AAC is not based on the filterbank design of MPEG Layer 2, but is a new development and uses the MDCT as the base transformation, just like Dolby Digital and Vorbis. With less complexity than MP3, better quality can be achieved at the same data rate.” (auto translated from wiki)

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