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roryf44560028
roryf44560028
Participant
December 20, 2017
Answered

Stablise motion with trackers goes choppy after changing frame rate

  • December 20, 2017
  • 1 reply
  • 466 views

Hello,

I'm having an issue trying to stablise a hyperlapse - Im using the stablise tracker and going through every frame selecting two points to track. Once I apply the trackers and render the composition plays back nicely and is really stable, however, when I change the composition frame rate from 30 to 24 the motion becomes unstable again.

Can anyone advise me as to what I'm doing wrong,

thanks.

Rory

This topic has been closed for replies.
Correct answer Rick Gerard

You have a couple of problems. I am hoping that the original comp was set to the same frame rate as the Hyperlapse. If not, that is part of your first problem. The second problem is that you don't understand the relationship between frame rate, time, keyframes and frames and overall time.

If the original comp frame rate matches the original frame rate of the Hyperlapse, check interpretation or the info to the right of the thumbnail in the Project Panel with the footage selected. If it does not match and you are happy with the stabilization then render an image sequence (preferable) or a visually lossless production format movie.

If you want to change the running time of the comp, changing the frame rate of the comp will not do anything to the length of the footage. Changing the frame rate of a comp will change the timing of the keyframes in relation to the original frames in the footage. Let me try and explain.

If you change the frame rate of the comp then the length of the imported clip does not change. One minute of 30 fps footage in a 30 fps comp is one minute long. One minute of 30 fps footage in a 24 fps comp is still one minute. The difference is that the frames have to be blended, doubled or otherwise merged to render the new frames in the comp. This puts the timing of your stabilization off for two reasons. First, keyframes are set at the start of each frame based on Time. When the composition frame rate is changed the keyframes are no longer at the start of each frame, they are at the original time of the start of the original frame.

Did you follow that? If you did not start a new comp at 30 fps that is 2 seconds long, add a solid and a position keyframe, move down 6 frames and set another keyframe. Zoom in on the timeline so you can see the individual frames. You will see that the keyframes are exactly at the start of each frame. Now change the comp frame rate to 24 fps and check out the position of the keyframes. They are no longer lined up and the keyframe that was on frame 6 is now happening at frame 5.

So you have at least 4 options.

  1. Render an image sequence or a suitable DI, re-interpret the footage to 24 fps so you can render a 24 fps movie and accept the time change and get every frame you stabilized in your final movie accepting the different playback time.
  2. Change the frame rate to 24 fps in the Render Settings of the Output Module and let the renderer blend the frames and accept the same time for your clip and blended frames.
  3. Nest your original stabilized 30fps comp in a new 24fps comp and accept frame blending.
  4. Start over by first interpreting the footage at the frame rate you want to use, match the comp to the frame rate, stabilize again and accept the time of the rendered composition.

I guess there are a half dozen other options. The important thing is that if you change the frame rate of a comp you will change the frame number of many of the keyframes applied to that footage. It's a bad idea.

I just thought of one more thing. If the total lengrh of the footage (Hyperlapse) is the concern then adjust the interpreted frame rate of the footage until you get the right length. Now put it in a comp that matches the frame rate of your final movie. If these frame rates differ you are going to get some blended frames but in most cases, and especially with Hyperlapse, nobody will ever see them.

1 reply

R
Community Expert
Rick GerardCommunity ExpertCorrect answer
Community Expert
December 20, 2017

You have a couple of problems. I am hoping that the original comp was set to the same frame rate as the Hyperlapse. If not, that is part of your first problem. The second problem is that you don't understand the relationship between frame rate, time, keyframes and frames and overall time.

If the original comp frame rate matches the original frame rate of the Hyperlapse, check interpretation or the info to the right of the thumbnail in the Project Panel with the footage selected. If it does not match and you are happy with the stabilization then render an image sequence (preferable) or a visually lossless production format movie.

If you want to change the running time of the comp, changing the frame rate of the comp will not do anything to the length of the footage. Changing the frame rate of a comp will change the timing of the keyframes in relation to the original frames in the footage. Let me try and explain.

If you change the frame rate of the comp then the length of the imported clip does not change. One minute of 30 fps footage in a 30 fps comp is one minute long. One minute of 30 fps footage in a 24 fps comp is still one minute. The difference is that the frames have to be blended, doubled or otherwise merged to render the new frames in the comp. This puts the timing of your stabilization off for two reasons. First, keyframes are set at the start of each frame based on Time. When the composition frame rate is changed the keyframes are no longer at the start of each frame, they are at the original time of the start of the original frame.

Did you follow that? If you did not start a new comp at 30 fps that is 2 seconds long, add a solid and a position keyframe, move down 6 frames and set another keyframe. Zoom in on the timeline so you can see the individual frames. You will see that the keyframes are exactly at the start of each frame. Now change the comp frame rate to 24 fps and check out the position of the keyframes. They are no longer lined up and the keyframe that was on frame 6 is now happening at frame 5.

So you have at least 4 options.

  1. Render an image sequence or a suitable DI, re-interpret the footage to 24 fps so you can render a 24 fps movie and accept the time change and get every frame you stabilized in your final movie accepting the different playback time.
  2. Change the frame rate to 24 fps in the Render Settings of the Output Module and let the renderer blend the frames and accept the same time for your clip and blended frames.
  3. Nest your original stabilized 30fps comp in a new 24fps comp and accept frame blending.
  4. Start over by first interpreting the footage at the frame rate you want to use, match the comp to the frame rate, stabilize again and accept the time of the rendered composition.

I guess there are a half dozen other options. The important thing is that if you change the frame rate of a comp you will change the frame number of many of the keyframes applied to that footage. It's a bad idea.

I just thought of one more thing. If the total lengrh of the footage (Hyperlapse) is the concern then adjust the interpreted frame rate of the footage until you get the right length. Now put it in a comp that matches the frame rate of your final movie. If these frame rates differ you are going to get some blended frames but in most cases, and especially with Hyperlapse, nobody will ever see them.

roryf44560028
roryf44560028Author
Participant
December 20, 2017

Hi Rick,

Thanks very much for such a detailed response - I appreciate the time you put into this.

I'm very new to AE and am just using it to stabilise my Hyperlapse.

My thoughts on going for 24 fps was so that my hyperlapse frames would run for a bit longer.

I was unaware of the interpret footage function, that has helped a lot.

I assumed AE would associate keyframes with the video frames rather than the time, this seems more intuitive to me - is there a way to change it?

Thanks again for your help,

Rory

R
Community Expert
Rick GerardCommunity Expert
Community Expert
December 20, 2017

In all Adobe apps keyframes are based on time. No way to change that. I am pretty sure that there is a script that will line them up with frames but that would not help the frame 6  becomes frame 5 problem. This is one of only a half dozen situations that I can think of that would foul up some animations.

Understanding time and frame rates are critical to working in any kind of video production. I often shoot VFX plates (shots) at 60 or even 120 FPS when the project is going to be delivered at 29.97 (most common) or 23.976. 24 is not really a video standard, it is a film standard and it not compatible with NTSC broadcast standards. The cable providers and broadcasters will slow down 24 to 23.976 and live with the minuscule pitch change in the audio. So why do I shoot VFX footage at a high frame rate? Because I get less motion blur which makes roto and procedural mattes easier to pull because it gives me more frames to work with for motion tracking and other things critical to VFX production. The motion blur can be matched after the composite is done and AE does a really good job of interpreting between frames when there are more than are necessary. It is also very important to slightly slow down or speed up a VFX shot for greater dramatic effect. That is easier to do if you shoot at a little higher frame rate to start with.

I am currently working on a Western. I had to speed up a scene where out leading lady draws a gun and even reposition her arm a bit using roto and puppet pins. Unfortunately, we did not shoot that shot at 29.97 or even higher and it would have been a lot easier to do the roto if I didn't have as much motion blur. It just takes time to get all of this stuff figured out. The most important thing about video though is that you cannot judge the quality of any clip by stepping through the shot a frame at a time. You have to watch it rendered using the delivery format at full size and full speed. A ram preview or test render will give you a pretty good idea how things are working, but the final quality determination has to be made using the delivery format and the delivery device.

One other thing I should mention because you are new to AE. AE is for creating shots. It is a terrible editing tool. Short sequences may be acceptable but any comp that covers more than a single idea, phrase or sentence will quickly become unmanageable. Do your editing in Premiere or any other NLE, build the shots you cannot build any other way in AE and you will make better movies with less effort.

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