The only way I know about is having the élastique Timestretch plug-in installed and use it as Track FX with automation so you could keyframe the timestretching (I don't mean the internal élastique Timestretch/Pitch Shift tool). I think (not sure though) my élastique plug-in once came with an installation of Sound Forge Pro.

but does it time it automatically for video & audio or you have to do it separately?

It only works separately. There's no other way in Vegas Pro.

use davinci resolve, it does speedramp optical flow slow motion synced with audio. edit with vegas, but create the slowmo inserts with resolve

It only works separately. There's no other way in Vegas Pro.

Still might work if I key the right framerates.. do you know how can I find this plugin? What is the exact name?

use davinci resolve, it does speedramp optical flow slow motion synced with audio. edit with vegas, but create the slowmo inserts with resolve

I was actually trying to find it in DR16 but I couldnt.. I went with retime curve, but it would not make the audio sound nice. What workflow you use?

The exact name of that plug-in is "élastique Timestretch", right as mentioned in the post above.

I just saw this plug-in not only is in the Pro version of Sound Forge but also in the Studio version, though I don't know if installing the Studio version would make that plug-in available for Vegas Pro. Maybe just try.

The exact name of that plug-in is "élastique Timestretch", right as mentioned in the post above.

I just saw this plug-in not only is in the Pro version of Sound Forge but also in the Studio version, though I don't know if installing the Studio version would make that plug-in available for Vegas Pro. Maybe just try.

will chack, but what I dont see from your photo is ability to add keyframes and smooth transition from normal to slow speed. this is what I need in order to create this sound effect

Yes, you need to use Track Automation for keyframing the élastique Timestretch parameters.