Speed up audio (i.e. shift pitch and tempo) and video? this is easy in WMM!

Firsly, I must say I'm very excited to see how 0.7.? has progressed recently (currently using 0.7.5 on kubuntu 9.04). I've been doing a lot of editing with Cinelerra and it is like using a sledgehammer to crack a nut. Most frustratingly (in Cinelerra), I can't seem to do something as simple as speed up by a factor of 2 (for example). You know, like a plain fast forward with the squeaky voices and everything - which would be trivial with film or VT.
Now I find that it is also non-trivial in Kdenlive - though I must say that the fact that when a clip is sped up it takes up less timeline space is a blessed relief (cinelerra is v. counter-intuitive on this).

Am I missing something? I simply want to take a short segment and make it run at double speed. I suppose that the audio system could be working in the frequency domain, rather than simple amplitude, but even so it shouldn't be difficult to convert to waveform and squash it up. I know how clever it is to change the pitch without changing the speed, and I know how clever it is to change the speed without changing the pitch, but I don't want that (and it never works properly anyway).

I see that I am offered the chance so change the audio clip speed in the same way that I can change the video clip speed, but when I do that the "thumbnail" disappears and I get silence. Is this what is supposed to happen? - maybe it hasn't been writen yet....

The "Rate scaler" seems to have the idea: it sounds right, but instead of speeding the whole clip up by a factor of n, it seems to chop the audio into (roughly) second-long chunks, then speed a chunk up by n, then play that chunk n times (i.e. in the second originally occupied by that chunk), then move on to the next second-long chunk, etc. I.e. overall the audio stays in the same "place". I am using this on .dv (exported from cinelerra).

This is trivial in Windoze Movie Maker ... I'd hate to think that it can do something that Kdenlive can't ;-)

Please understand that this isn't an outraged demand, I'm just surprised that such a simple thing isn't present and I wonder if instead I'm just being dense (of course, both might be true).

Any thoughts?

Share and Enjoy...

Not exactly, though it would be a great feature.
I want to be able to produce sped-up AV in the finished product, just as though I was winding film through a projector too quickly.
I guess I'm going to have to chop it into sections and render each one in turn and hope I don't have to change anything later....

I don't know if it's that what you search, but I can change the speed of Video and Audio in doing so:

- Right Click on the video you want to speed up, in the timeline menu
- Choose the option with "Speed" in it, should be the second option
- enter in percent how much faster or slower you want to have it

That's it :)

EDIT:
Whoops, now I see what the problem is... I'd need a solution for that one too.

Yes, it looks like the speed effect on video is muting audio.

Splitting and ungrouping audio from video would allow to apply a matching audio effect.
But as mentioned before, the only candidate for an audio playback rate and time length adjustament similar to the speed effect, rate scaler, behaves kind of weird. (Is there some sort of doku about this audio effect ? What's its purpose ? )
Or is this effect supposed to do the job (according to it's name) and we're faced with a bug ?

Ideally, I'd love to see an option inside the video speed effect, which allows for corresponding, "speed" adjusted audio (tape) playback. This would eliminate redundant rate change specification and should be easier to handle at the same time.

Toby

Me too, I'd like to see this function added to Kdenlive. I think it might be a tough one to implement: The audio must scale its sample rate to match the increasing speed of the clip, and I think that might be tricky to do right. Maybe one of the devs can clarify ?

Best,

dp

What's required is basically the well known resample operation.
And there are proven open source implementations out there, e.g. libsamplerate.

But since kdenlive/MLT is able to perform resampling during rendering, it's obviously already implemented in some form. It just needs to be hooked in at the right place.

At the moment, I'm still assuming that "rate scaler" should do the trick and there's a bug in this audio effect. But I'd probably better off filing a bug report ...

Toby

Hey, i just ran into this bug now. Speeding up clip, even by 1%, mutes sound.

No, sound muting is normal.

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