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My question is simple: I can change the speed of video in the sequencer, but not audio. Will this feature ever be supported in Blender? If there is no such plan, is there some hints of implementing that in plugins?

I haven't looked a lot into Blender API yet, but I would like to do it "the Blender way" if there is one. Currently, I have to render only the audio, edit that using other applications (eg. Audacity), and import back. This is tedious. The simplest way might be just automating this, but I would prefer not to touch the core of Blender (i.e. modify things like Blender source code).

Update

I now have a procedure of simulating this. First, assume I have a segment of audio/video to be accelerated 2X. First, I hard cut out both the audio and video (try to get an even number of frames, call it F. The beginning of the cut is B, and the end E), then do the speed effects on video as usual. Then, on the cut out strip of audio, I change pitch to 2, and change the Start frame of Trim Duration(hard) to the half of current value, then hard cut again at B+F/2 (or change its length to F/2). This will allow you to speed up both the audio and video to twice, but without the need to render the audio strip separately. Very tedious, but very procedural, using only Blender functions. It might be easy to either automate it using a plugin or implement it right into the core. I will check Blender API and code, too.

Note: It seems that I must change pitch first, then change starting point, then change duration

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    $\begingroup$ If it's not there, asking that feature should help this to happen... :) see blender.stackexchange.com/questions/1190/… $\endgroup$
    – m.ardito
    Commented Oct 25, 2015 at 14:08
  • $\begingroup$ It seems you can automate your workflow in python. $\endgroup$
    – Samoth
    Commented Nov 18, 2015 at 11:45
  • $\begingroup$ I am not satisfied since it doesn't change speed AND pitch -- Python + Blender cannot do that, at least not with a bunch of temporary files. I am digging through blender and trying to hack in this feature by hacking Audaspace, which is what Blender use for audio fx/mixdown $\endgroup$
    – Carl Dong
    Commented Nov 18, 2015 at 15:07
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    $\begingroup$ Rather than updating your question with your answer you should answer your own question. ;-) $\endgroup$
    – Samoth
    Commented May 18, 2016 at 8:50

2 Answers 2

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You can change an Audio Strips speed by changing/animating it's pitch. Though it has to be done independant from your videos Speed Control strip.

Animated Pitch Value

And it will (as it is labled) change your pitch. So if you want to maintain the pitch but only change the speed that has to be done in another audio editor like Audacity.

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  • $\begingroup$ This doesn't seem to work in Blender 2.8 $\endgroup$
    – reubenjohn
    Commented Mar 13, 2020 at 14:31
  • $\begingroup$ Maybe you should open a bug report then... $\endgroup$
    – Samoth
    Commented Mar 14, 2020 at 1:11
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In Blender 4 or later versions, simply press I to add a retiming keyframe to the selected strip within Video Sequencer Editor.

Otherwise, click on Strip on the menu bar, then click on Retiming > Add Retiming Keyframe.

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