Am 28.04.2021 um 23:34 schrieb Bo Berglund:
On Wed, 28 Apr 2021 11:35:47 +0200, Michael Koch <astroelectro...@t-online.de>
wrote:
I had tested this (which I found by googling) before I posted:
ffmpeg -i input20.mp4 -filter:a "atempo=1.25" -vn output20.mp4
There were no errors displayed but the resulting file *ONLY* contains the audio
part, I neeed both and the audio change must not change the length or lipsync of
the file.
Sure, that's because -vn means "no video output". Just remove this
option and then your output file will contain audio and video.
OK, that included the video...
But now there is no lip-sync at all. Seems to drift longer apart during the
video playing. Audio and video running at different speeds.
The atempo filter changes the length of the audio track, while keeping
the pitch and the sample rate constant. As shown in the 5th command line
in chapter 3.4 in my book.
If you want to change only the audio pitch (and keep the sample rate and
length constant), you must use a combination of asetrate, atempo and
aresample filters. That's the 2nd command line in that chapter.
Michael
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