To change the key signature of a song

[suntong]

Suppose that a song was originally sang in F调, I want to be able to use ffcvt to change it to a different 调, like D调, etc.

[suntong]

Done, with f6ee9d5:

ffcvt/test/ffcvt_test.txt

Lines 38 to 39 in f4b59a5

	-tkf Transpose song's key from (e.g. C/C#/Db/D etc) (FFCVT_TKF)
	-tkt Transpose song's key to (e.g. -tkf C -tkt Db) (FFCVT_TKT)

For usage examples, see

ffcvt/test/test-all.sh

Lines 27 to 30 in f4b59a5

	echo '# Test transposing different keys' | tee -a /tmp/ffcvt_test.txt
	$FFCVT -t x264-mp3 -n -f StreamSample.mkv -w /tmp -tkf F -tkt D -vn >> /tmp/ffcvt_test.txt 2>&1
	$FFCVT -t x264-mp3 -n -f StreamSample.mkv -w /tmp -tkf 'F#' -tkt Db -vn -abr 72k >> /tmp/ffcvt_test.txt 2>&1
	$FFCVT -t '' -n -f StreamSample.mkv -tkf Gb -tkt 'A#' -vn -abr 72k -aes libmp3lame -ext _.mp3 >> /tmp/ffcvt_test.txt 2>&1

The first command, -tkf F -tkt D is transposing from 'F' major to 'D' major.

Results/commands:

ffcvt/test/ffcvt_test.txt

Lines 220 to 248 in f4b59a5

	# Test transposing different keys
	Transposing from 'F' (349.23) to 'D' (293.66)
	== Transcoding: StreamSample.mkv
	] ffmpeg -i StreamSample.mkv -vn -c:a libmp3lame -b:a 256k -q:a 3 -af atempo=349.23/293.66,asetrate=44100*293.66/349.23 /tmp/StreamSample.mp4
	ffcvt: to execute -
	ffmpeg -i StreamSample.mkv -vn -c:a libmp3lame -b:a 256k -q:a 3 -af atempo=349.23/293.66,asetrate=44100*293.66/349.23 /tmp/StreamSample.mp4
	Transcoding completed in xxx ms
	Org Size: 0 MB
	New Size: 0 MB
	Saved: 0%
	Transposing from 'F#' (369.99) to 'Db' (277.18)
	== Transcoding: StreamSample.mkv
	] ffmpeg -i StreamSample.mkv -vn -c:a libmp3lame -b:a 72k -q:a 3 -af atempo=369.99/277.18,asetrate=44100*277.18/369.99 /tmp/StreamSample.mp4
	ffcvt: to execute -
	ffmpeg -i StreamSample.mkv -vn -c:a libmp3lame -b:a 72k -q:a 3 -af atempo=369.99/277.18,asetrate=44100*277.18/369.99 /tmp/StreamSample.mp4
	Transcoding completed in xxx ms
	Org Size: 0 MB
	New Size: 0 MB
	Saved: 0%
	Transposing from 'Gb' (369.99) to 'A#' (466.16)
	== Transcoding: StreamSample.mkv
	] ffmpeg -i StreamSample.mkv -vn -c:a libmp3lame -b:a 72k -af atempo=369.99/466.16,asetrate=44100*466.16/369.99 StreamSample_.mp3
	ffcvt: to execute -
	ffmpeg -i StreamSample.mkv -vn -c:a libmp3lame -b:a 72k -af atempo=369.99/466.16,asetrate=44100*466.16/369.99 StreamSample_.mp3

In summary, to transpose a .mp3 file:

ffcvt -t '' -ext _.mp3 -tkf X -tkt Y -abr 72k -f input.mp3
mpv --force-window input_.mp3

[suntong]

Refs:

Transposition: Changing Keys
https://www.earmaster.com/music-theory-online/ch06/chapter-6-4.html

Changing the key of a piece of music is called transposing the music.

As to how to transpose --

Musical scale, musical note frequencies
https://github.com/suntong/ffcvt/wiki/Ref:-Musical-scale,-musical-note-frequencies