Lowering the FPS without droping frames? (and correcting sound)

drdespair wrote on 7/11/2002, 5:02 PM
Hello,

I would like to take a 25 fps video clip and slow it down to 24 fps without removing the 1 frame, and keeping the sound pitch correct. (I am shure the sound would require some re pitching) can anyone help me with how this can be accomplished?

Thanks!

Best Regards,

Denis

Comments

Chienworks wrote on 7/11/2002, 6:05 PM
This takes a few steps. First, go to File / Properties and set the Frame rate for the project to 24. This will help make sure that the output file is 24fps.

I'm assuming that the clip in question is the only event you have on the timeline, and that it starts at 00:00:00.00. The difference in speed from 25fps to 24fps is 0.96. Divide the current length of the event by 0.96 to find out what the new length is. If the original length is, for example, 2:19.14 (139.56 seconds), then the new length will be 2:25.09 (145.375 seconds). Place the cursor at this location on the timeline for easy snapping. Place the mouse at the right edge of the clip and you will see the pointer change to a little box with a double-headed arrow. Hold the Ctrl key down and drag the end of the clip to the cursor position (it will snap there).

Render the event to a new file. You will have to use the default template as DV doesn't support 24fps.

This is just one quick simple method. I'm sure others out there have their own methods that they will share.
AFSDMS wrote on 7/11/2002, 6:46 PM
Since you are on a roll (:-). . .

I have a clip where I am extending the opening fade in by starting with a freeze frame and slowly ramping up to full frame rate using the velocity envelope. As I quickly learned, the associated audio starts at the very first frame and continues at speed, thus the sound preceeds the picture. Other than looking for a visual sync cue, is there an easy way, or do you have suggestions, for syncing this up?

Thanks much.

Wayne Munn
Chienworks wrote on 7/11/2002, 7:56 PM
If you really need to preserve audio/video sync, then velocity envelopes are probably gonna be a nightmare. You can instead split the clip where you want the velocity to change, and then Ctrl-Drag to stretch/shrink the section that has to be a different speed. You won't have as fine control, but this will keep everything in sync.
SonyDennis wrote on 7/11/2002, 10:26 PM
Chienworks:

Fantastic description, spot on.

The only thing I can add is to double-check the event properties for the audio event to make sure the Time stretch / pitch shift method is set to "Change length, preserve pitch" since, in this case, you want to preserve pitch. You can experiment with the Crossfade property and pick the best one for your type of audio material.

And then be amazed that you can pull off such a cool thing on your PC with Vegas; hardware to do this used to cost a lot of money <g>!

///d@
Chienworks wrote on 7/11/2002, 11:07 PM
Dennis, i've got a curious question ... Obviously media files contain the frame rate encoded within them, and players & editors read this information to know how fast to step through the frames. Is there any way to just simply change that value? I would have found this very handy a while ago when using a capture utility that allowed frame by frame capture for animation. I wanted to produce a 30fps animation, but this capture utility only encoded the .avi files at 12fps (which obviously wasn't true anyway since i was capturing the frames about 5 a minute). I wish i could have just changed that 12fps value in the file to 30, but couldn't find any way to do it except the procedure i outlined above.
SonyDennis wrote on 7/11/2002, 11:19 PM
There are utilities for changing the frame rate in an AVI file, and (I think) Sound Forge 4.5 and 5 could do it with some finagling.

In Vegas, the event property "undersample rate" will let you modify a frame rate down but not up. Your rate change trick can be used to do "up".

///d@
SonyDennis wrote on 7/11/2002, 11:22 PM
wmunn:

I have two solutions to the velocity ramp with audio sync, but no matter how I word them, the forum software isn't letting me post them. Has anyone else had this happen to them? I'll try posting them from my work machine tomorrow.

Update: Post from work machine worked great, it's below.

///d@
Chienworks wrote on 7/11/2002, 11:27 PM
I've had a few cases in which i click the Reply button and get no "Body:" box to type in. Usually if i go to a different thread and then come back later on i'll get the box.
SonyDennis wrote on 7/12/2002, 8:48 AM
wmunn:

Regarding the velocity ramp-up with audio sync, I've had to do exactly this, and I've got two ways to do it:

Method 1
1. Options > Prefs > Video - turn on source frame numbers.
2. Ungroup the A/V events.
3. Split the video event at the spot where you want it to be 100% velocity. Notice the matching frame numbers at the split.
4. Slip Trim (Alt + edge drag) the first video event's left edge to the left to where you want it to start. Notice the frame numbers no longer match at the split.
5. Add a velocity envelope to the first event. Create a point in the middle, drag it to the right edge, right-click on it and set it to "Normal" speed.
6. Drag the left envelope point down until the frame numbers at the split match again. You can make the track taller to get more envelope adjustment range. If you have to go to negative velocities, you Slip-Trimmed too far or Split too far to the left.
7. Now, when you play, the velocity will gradually increase, and when you get to the 100% spot, the frames match and the audio will be in sync.
8. If you want to tweak the locations, Slip Trim again, move the 100% point to the right edge again, and re-adjust the first envelope point for matching frame numbers again. You can also Roll the edit point (Ctrl+Alt+edge drag) if needed.

Method 2
1. Options > Prefs > Video - turn on source frame numbers.
2. Ungroup the A/V events.
3. Write down the end (rightmost) video frame number.
4. Add velocity envelope to video event, set slow start point on left, and a 100% point where you want it. Play with the video until you get the rate ramp how you like it.
5. Trim the right edge of the video until it ends on the frame it used to end on (the one you wrote down). You might want to zoom in on the timeline to get this accurate.
6. Move the audio event so it ends where the video event ends, which should put it back in sync with the 100% velocity parts.

Each method has it's strong points, depending on how you like to work.

///d@