[tebasuna51]

Originally Posted by Meow

Not familiar with 120fps YouTube videos?

Yes, then correct me if next comments are wrong.

How it works is that you have a 120fps video clip, you slow it down to exactly half, and render as 60fps.

For instance you have a video clip with 120 frames than played at 120 fps have a real duration of 1 second.

And you change the fps to 60 to obtain a wrong duration of 2 seconds for these 120 frames.

Then playback with YouTube on 2x speed and the result is 120fps.

When playback at 2x you recover the correct duration of 1 second for these 120 frames.

Now you have the real audio of 1 second of duration than want to mux to fake 60 fps video.

I don't know what do the playback 2x with the audio, even some players can mute the audio when select a double speed for the video.

But, in theory, the change of video fps to half (120 -> 60 fps) is equivalent to change the audio samplerate to half (48000 -> 24000 Hz).

Then the 48000 samples of 1 second real audio are played in 2 seconds at 24 KHz.
Maybe the player at 2x recover the original samplerate and play the 48000 samples in 1 second lossless.

You can try this solution. Remember, is change the samplerate, not resample the audio or change the duration.

Resample:
When you resample 48000 samples 48 KHz to 24 KHz you obtain 24000 samples with 1 second of duration. Lossy conversion.

Change duration:
When you drag the audio with 48000 samples 1 second in Vegas, over a 2 seconds video, it convert the 48000 samples in 96000 samples to obtain 2 seconds played at 48 KHz. Lossy conversion.

And we need 48000 samples 48 KHz = 1 second, the same 48000 samples played at 24 KHz = 2 seconds.
Lossless conversion (the samples are untouched).
We hope than playback at 2x recover the real duration without modify the samples.

I don't know if Vegas can do it, but yes any audio editor (Audition, SoundForge, Goldwave, Audacity,...).