[FFmpeg-user] Changing video speed

JD jd1008 at gmail.com
Mon Jan 21 19:09:51 EET 2019

On 01/21/2019 06:42 AM, Moritz Barsnick wrote:
> On Sat, Jan 19, 2019 at 14:55:55 -0700, JD wrote:
>> I have a video that was sped up and now the voice is like
>> that of cats in cartoons.
>> How can I at least lower the pitch back to normal?
>> Since the whole video was sped up, I would rather
>> slow down the whole video (video and audio) AND lower
>> the pitch back to near normal?
> There's a wiki page covering this:
> https://trac.ffmpeg.org/wiki/How%20to%20speed%20up%20/%20slow%20down%20a%20video
> (There's a part saying "Using a complex filtergraph, you can speed up
> video and audio at the same time:". IMO, you can also do this with
> separate "simple" filters, using "-vf" and "-af".)
> Carl Eugen failed to mention that the setpts filter doesn't change the
> audio speed. The audio example in the wiki, using "atempo", changes the
> speed while _maintaining_ the pitch. To stretch the audio _including_
> pitch change, you need to instead change the sample speed with the
> "asetrate" filter, and re-adapt the output sample rate (because your
> output file will require a sane sample rate such as 44.1k or 48k) with
> "-ar".
> E.g. to reduce the speed of the audio to 0.8x of the given input,
> assuming an input sample rate of 48000k:
> $ ffmpeg -i input -af asetrate=38400 -ar 48000 output
> (38400 is 0.8 * 48000. I wish asetrate would understand an "input
> sample rate" variable.)
> Moritz________________________

Hi Moritz,
Once I determine what the videos current rates are,
for vid and aud, and let's assume I want to low down both
by a factor of 30%, and I multiply 0.3 by each rate (aud and vid),
and come up with 2 values that re 30% less than current vid,
would my command line look like this: ?

ffmpeg -i my-vid.mp4 -af asetrate newRate -ar 48000  -vf vsetrate 
newRate -vr ????? Output

How would I specify the value for the '?????'


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