[FFmpeg-user] Possible to change pitch of audio in a downloaded mp4 file?

[Bo Berglund]

On Wed, 28 Apr 2021 09:03:26 +0200, Michael Koch <astroelectronic at t-online.de>
wrote:

>Am 28.04.2021 um 08:51 schrieb Bo Berglund:
>> Sometimes when I download a video it turns out to have some issues that has
>> raised the audio pitch of the video making it not so enjoyable to watch/hear.
>> So I wonder if there is an ffmpeg command that can modify the pitch of the audio
>> without changing the playback speed or lipsync?
>
>Yes, this is possible with a combination of asetrate, atempo and 
>aresample filters.
>See chapter 3.4 in my book:
>http://www.astro-electronic.de/FFmpeg_Book.pdf
>

Thanks for the book! It has many useful items.

But chapter 3.4 seems to deal only in modifying an audio file whereas I am
talking about an mp4 video with both audio and video content.
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.

I already have a script to change lipsync using ffmpeg this way (shifting audio
350 ms here):

ffmpeg -hide_banner  -i input.mp4 -itsoffset -0.35 -i input.mp4 -map 1:v -map
0:a -c copy output.mp4

Is this basically what one has to do, specifying the input twice?
I am not really understanding how all the ffmpeg arguments do work...


-- 
Bo Berglund
Developer in Sweden